Interaction of polymers with bile salts - Impact on solubilisation and absorption of poorly water-soluble drugs

Formulating poorly soluble drugs with polymers in the form of solid dispersions has been widely used for improving drug dissolution. Endogenous surface-active species present in the gut, such as bile salts, lecithin and other phospholipids, have been shown to play a key role in facilitating lipids and poorly soluble drugs solubilisation in the gut. In this study, we examined the possible occurrence of interactions between a model bile salt, sodium taurocholate (NaTC), and model spray dried solid dispersions comprising piroxicam and Hydroxypropyl Methylcellulose (HPMC), a commonly used hydrophilic polymer for solid dispersion preparation. Solubility measurements revealed the good solubilisation effect of NaTC on the crystalline drug, which was enhanced by the addition of HPMC, and further boosted by the drug formulation into solid dispersion. The colloidal behaviour of the solid dispersions upon dissolution in biorelevant media, with and without NaTC, revealed the formation of NaTC-HPMC complexes and other mixed colloidal species. Cellular level drug absorption studies obtained using Caco-2 monolayers confirmed that the combination of drug being delivered by solid dispersion and the presence of bile salt and lecithin significantly contributed to the improved drug absorption. Together with the role of NaTC-HPMC complexes in assisting the drug solubilisation, our results also highlight the complex interplay between bile salts, excipients and drug absorption.

Ice recrystallization inhibition activity in bile salts

Ice recrystallization inhibitors are novel cryoprotective agents that can reduce the freezing damage of cells, tissues, and organs in cryopreservation. To date, potent ice recrystallization inhibition (IRI) activity has been found on antifreeze (glyco)proteins, polymers, nanomaterials, and a limited number of chemically synthesized small molecules. This paper reports a relatively potent IRI activity on a group of small biological molecules - bile salts. The IRI activity increased as the number of hydroxyl groups decreased in bile salts. Among sodium cholate (NaC), sodium deoxycholate (NaDC), sodium chenodeoxycholate (NaCC), and sodium lithocholate (NaLC), the least hydrophilic NaLC at a concentration of 25.0 mM entirely blocked the ice growth in phosphate-buffered saline (PBS) under test conditions. The IRI activity of bile salts was not related to viscosity or gelation. No IRI activity was found below the critical micelle concentration. The IRI activity was independent of liquid crystal formation. No ice shaping and thermal hysteresis were observed on any bile salts, but NaC and NaLC could increase the ice nucleation temperature. The findings add bile salts to the existing material list of ice recrystallization inhibitors.

New β-carboline derivatives containing imidazolium as potential VEGFR2 inhibitors: synthesis, X-ray structure, antiproliferative evaluations, and molecular modeling

A series of new β-carboline derivatives containing an imidazolium moiety were designed and synthesized via the reaction of β-carboline-1-carboxaldehydes, acetyl chloride, primary amine, and formaldehyde. The antitumor activity of the synthesized compounds was examined against lung carcinoma (A549), gastric carcinoma (BGC-823), murine colon carcinoma (CT-26), liver carcinoma (Bel-7402) and breast carcinoma (MCF-7) cells. The results indicated that most compounds exhibited significant antiproliferative activity, in some cases greater than that of cisplatin, and compound 3z was found to be the most potent antiproliferative agent against A549, BGC823, CT-26, Bel-7402 and MCF-7 cell lines with an IC50 value of 2.7 ± 0.4, 2.7 ± 0.6, 2.4 ± 0.2, 3.2 ± 0.2, and 5.6 ± 0.3 μM, respectively. Combined with favorable in vitro potency, the antitumor efficacies of the selected compounds in mice were also evaluated. Compound 3z exhibited potent antitumor activity with a tumor inhibition rate of 48.6% in sarcoma 180 models. Preliminary investigations on the mechanisms of action revealed that compound 3z could dramatically inhibit EA.hy926 cell tube formation in a dose-dependent manner. Further investigation of the preliminary mechanism of action demonstrated that compound 3z had obvious angiogenesis inhibitory effects in the chicken chorioallantoic membrane (CAM) assay. The results of the docking study showed a good fitting of the new compounds 3o and 3z to the active site of VEGFR-2 with a docking score energy of -11.31 kcal per mole and -11.26 kcal per mole, respectively.

Potential Hypolipidemic Effects of Banana Condensed Tannins Through the Interaction with Digestive Juice Components Related to Lipid Digestion

An in vitro intestinal model was used to evaluate the impact of banana condensed tannins (BCT) on the digestion of lipids (fat and cholesterol). BCT significantly suppressed the digestion of fat and cholesterol by interacting with digestive juice components. The interactions of BCT with a digestive juice mixture and its components (including bile acid, lipase, cholesterol esterase, CaCl₂, NaCl, and cholesterol) were analyzed using turbidity, isothermal titration calorimetry, particle size distribution, zeta potential, and molecular docking analyses. The results showed that BCT reduced the digestion of lipids mainly via interaction with lipase, cholesterol esterase, bile acid, and cholesterol. Electrostatic CT-calcium ion complexes might reduce the extent of lipid digestion by decreasing the surface area of the lipid droplets exposed to the enzymes. This research provides valuable insights into the molecular mechanisms of the interaction of BCT with digestive juice components related to lipid digestion that may affect the rate and extent of lipid digestion.

The kinetics of formation of resveratrol-β-cyclodextrin-NH2 and resveratrol analog-β-cyclodextrin-NH2 supramolecular complexes

The determination of the kinetics of inclusion processes is significant for the application of inclusion complexes as carriers for bioactive molecules. We determined the kinetic parameters of inclusion between modified β-cyclodextrin (β-CD-NH₂) and the polyphenols resveratrol (RES) and its structural analog (RESAn1), using the real-time analysis of surface plasmon resonance. The association and dissociation rate constants (k_a and k_d) showed that RESAn1 inclusion and its dissociation from β-CD-NH₂ were faster than a similar process for RES ( [Formula: see text]  = 3.10∙10⁴ ± 0.14 M^-1s^-1, [Formula: see text] =1.87∙10³ ± 0.11 M^-1s^-1; [Formula: see text] =0.39 ± 0.02 s^-1, [Formula: see text] =0.30 ± 0.02 s^-1, at 25 °C). The activated complex formation was also affected by the structural differences between the polyphenols, as showed by the activation energies of the association step ( [Formula: see text] 14.81 ± 0.64 kJ∙mol^-1, [Formula: see text] -15.01 ± 0.75 to 82.35 ± 4.47 kJ∙mol^-1). These effects of polyphenol structural differences are due to the desolvation process of interacting molecules. These results elucidate the role of small group to the dynamics of the molecular inclusion of β-CD.

Probing the Hydrogen Bond Involving Acridone Trapped in a Hydrophobic Biological Nanocavity: Integrated Spectroscopic and Docking Analyses

Spectroscopic analyses reveal that acridone (AD) penetrates through the structure and enters the hydrophobic cavity of the protein β-lactoglobulin (βLG). Although the protein contains two tryptophan (Trp) residues, AD interacts with only one (Trp-19), which is authenticated by the appearance of a single isoemissive point in TRANES. Alteration in the secondary structure of the protein while AD pierces through βLG is evident from the circular dichroism spectroscopic study. The ground-state interaction between AD and βLG is proven from the UV-vis spectroscopic study and the static nature of quenching of intrinsic fluorescence of the protein by the ligand. The steady-state fluorescence study in varied temperatures indicates the involvement of hydrogen bonding in the ligand-protein interaction. Further, the time-resolved fluorescence anisotropy study gives a hint of the presence of a hydrogen bond in AD-βLG interaction, which possibly involves the rotamers of Trp-19. In fact, the idea of involvement of rotamers of Trp-19 is obtained from the increase in fluorescence lifetime of βLG in the presence of AD. The docking study agrees to the involvement of hydrogen bonding in AD-βLG interaction. The direct evidence of hydrogen bonding between Trp and AD is obtained from the laser flash photolysis studies where the signature of formation of ADH^• and Trp^• through hydrogen abstraction between Trp and AD, loosely bound through hydrogen bonding, gets prominence. Thus, binding of AD to βLG involves hydrogen bonding in a hydrophobic pocket of the protein.

Revealing the dynamics and energetics of interaction of a cationic biological photosensitizer within a bile salt aggregate

The present investigation reports a detailed characterization of the interaction of a cationic photosensitizer, phenosafranin (PSF) with sodium deoxycholate (NaDC) bile salt aggregates based on spectroscopic and calorimetric techniques. Our explicit spectroscopic results not only establish the occurrence of PSF-NaDC binding interaction, but also reveal marked lowering of micropolarity at the interaction site (E_T(30) = 55.97 kcal mol^-1 in the presence of NaDC as compared to E_T(30) = 63.1 kcal mol^-1 in bulk aqueous buffer). A thorough mathematical analysis of the fluorescence depolarization results based on the two-step and wobbling in cone model yields critical insight into the complex rotational relaxation dynamics of the bound drug. The impartation of motional restriction on the PSF molecules within the bile salt aggregates is evidenced from enhancement of average rotational correlation time from <τ_r> = 136 ps in aqueous buffer to 1.11 ns with added NaDC (8.0 mM). This is further supported from a high value of the generalized order parameter (S = 0.81) as well as the diffusion coefficient (D_w = 1.40 × 10¹² s^-1). Furthermore, our extensive calorimetric investigation unveils the complicated thermodynamics of the interaction process in terms of predominant entropic contribution over the enthalpic part in the lower temperature regime (TΔS = 18.84 ± 1.13 kJ mol^-1, ΔH = -5.82 ± 0.35 kJ mol^-1 at 288 K) with subsequent reversal of the relative contributions with increasing temperature (TΔS = 7.54 ± 0.39 kJ mol^-1, ΔH = - 17.09 ± 0.90 kJ mol^-1 at 318 K). The instrumental role of the hydrophobic effect underlying the PSF-NaDC interaction is characterized by a negative heat capacity change (ΔC_p = -364 J mol^-1 K^-1). An intriguing thermodynamic feature in terms of enthalpy-entropy compensation (with increasing temperature ΔG remains almost constant while ΔH and TΔS vary significantly) aptly corroborates the aforesaid argument and establishes an appreciable hydrophobic contribution to the overall binding energies.

Characterizing the Interactions of Dietary Condensed Tannins with Bile Salts

This study aimed to reveal the mechanisms underlying the interaction between condensed tannins (CTs) and bile salts. The interaction mechanism was analyzed by transmission electron microscopy, exposure to various physicochemical conditions, electrophoresis, fluorescence spectroscopy, isothermal titration calorimetry, and molecular modeling. A new complex was formed from CTs and bile salts. The complex showed a negative enthalpy change and a positive entropy change, demonstrating that the main thermodynamic driving force was both entropy and enthalpy and indicating that binding occurred through hydrogen bonds and hydrophobic interactions. The analysis of the effects of CTs on the stability and digestion properties of bile salt emulsions indicated that CTs were able to inhibit lipid digestion to an extent. Our findings may provide evidence that foods rich in CTs offer health benefits by aggregating with bile salts and reducing the absorption of fat.

Probing the molecular interactions between pharmaceutical polymeric carriers and bile salts in simulated gastrointestinal fluids using NMR spectroscopy

The number of poorly soluble new drugs is increasing and one of the effective ways to deliver such pharmaceutically active molecules is using hydrophilic polymers to form a solid dispersion. Bile salts play an important role in the solubilisation of poorly soluble compounds in the gastrointestinal tract (gut) prior to absorption. When a poorly water-soluble drug is delivered using a hydrophilic polymer based solid dispersion oral formulation, it is still unclear whether there are any polymer-bile salt interactions, which may influence the drug dissolution and solubilisation. This study, using two widely used hydrophilic model polymers, Hydroxypropyl methylcellulose (HPMC) and polyvynilpirrolidone (PVP), and sodium taurocholate (NaTC) as the model bile salt, aims to investigate the interactions between the polymers and bile salts in simulated fed state (FeSSIF) and fasted state (FaSSIF) gut fluids. The nature of the interactions was characterised using a range of NMR techniques. The results revealed that the aggregation behaviour of NaTC in FaSSIF and FeSSIF is much more complex than in water. The addition of hydrophilic polymers led to the occurrences of NaTC-HPMC and NaTC-PVP aggregation. For both systems, pH and ionic strength strongly influenced the aggregation behavior, while the ion type played a less significant role. The outcome of this study enriched the understanding of the aggregation behaviour of bile salts and typical hydrophilic pharmaceutical polymers in bio-relevant media. Due to the high surface-activity of the bile salts and their ability to interact with polymers, such aggregation behaviour is expected to play a role in drug solubilisation in the gut when the drug is delivered by hydrophilic polymer based dispersions.

Association and sequestered dissociation of an anticancer drug from liposome membrane: Role of hydrophobic hydration

Herein, the interaction of a potent anticancer drug (Sanguinarine, SG) with dimyristoyl-l-α-phosphatidylglycerol (DMPG) liposome membrane has been investigated at physiological pH. The spectroscopic fluorescence decay results demonstrate a modification of the photophysics of SG within DMPG-encapsulated state leading to preferential stabilization of the iminium ion over the alkanolamine form. This suggests a key role of electrostatic force underlying the interaction. The complex dependence of the thermodynamic parameters on temperature yields a unique finding of a positive heat capacity change (ΔC_p) indicating the signature of hydrophobic hydration. The study also demonstrates the application of β-cyclodextrin (βCD) as a prospective host system resulting in release of the DMPG-bound drug. A calorimetric exploration of the DMPG-βCD interaction reveals an intrinsically complex thermodynamics of the process leading to ΔC_p > 0 and thus marking the instrumental role of hydrophobic hydration which follows that the DMPG-βCD interaction is accompanied with burial of polar molecular surfaces. A systematic investigation of the diffusion of the drug within various microheterogeneous environments by Fluorescence Correlation Spectroscopy (FCS) categorically reinforces our arguments.

Improved Biopharmaceutical Properties of Oral Formulations of 1,2,4-Thiadiazole Derivative with Cyclodextrins: in Vitro and in Vivo Evaluation

The synthesized 1,2,4-thiadiazole derivative displaying biological activity has low aqueous solubility and dissolution rate. Novel oral formulations of thiadiazole with β- and hydroxypropyl-β-cyclodextrins were obtained by grinding and freeze-drying methods with the purpose to improve the aqueous solubility. Complex formation of 1,2,4-thiadiazole derivative with cyclodextrins was confirmed by means of solid-state ¹³C MAS CP/TOSS NMR. Solubility, dissolution rate and permeability of the solid inclusion complexes were evaluated in different biorelevant media (SGF, FaSSGF, FaSSIF) simulating the conditions in the gastrointestinal tract. It was demonstrated that the content of biorelevant media affects the properties of the inclusion complexes. In particular, solubilizing effect of cyclodextrins became less pronounced when the micelles of taurocholic acid and lecithin are formed in the dissolution media. The inclusion of thiadiazole into cyclodextrin cavity is in competition with its partitioning into the micelles and this should be taken into account when the in vivo behavior is predicted. The results of in vitro and in vivo experiments were found to be in agreement and showed the highest solubility, dissolution rate and bioavailability of the freeze-dried complexes of thiadiazole with hydroxypropyl-β-cyclodextrin. These complexes can be proposed as more effective dosage forms for oral administration.

Cu-catalyzed mild and efficient oxidation of THβCs using air: application in practical total syntheses of perlolyrine and flazin

A mild, efficient and environmentally benign method for synthesis of aromatic β-carbolines via Cu(ii)-catalyzed oxidation of 1,2,3,4-tetrahydro-β-carbolines (THβCs) was developed, in which air (O₂) was used as the clean oxidant. This method has advantages such as environmentally friendliness, mildness, very good tolerance of functional groups, high yielding and easy experiment operation. In addition, this new methodology was successfully applied in the efficient and practical total syntheses of β-carboline alkaloids perlolyrine and flazin.

A mild, efficient and ecofriendly method for synthesis of β-carbolines via Cu-catalyzed aerobic oxidation of 1,2,3,4-tetrahydro-β-carbolines (THβCs) was developed. In addition, this method was successfully applied in the practical total syntheses of perlolyrine and flazin.

Differential Perturbation of the Protrotropic Equilibrium of a Biological Photosensitizer within Bile Salt Aggregates of Varying Hydrophobicity: A Fluorimetric Investigation

The present work reveals the binding interactions of a credible cancer cell photosensitizer, harmane (HM), with some selected bile salt aggregates of dissimilar hydrophobicity viz. sodium deoxycholate (NaDC), sodium cholate (NaC) and sodium taurocholate (NaTC). The explicit variation of the prototropic equilibrium of the photosensitizer both in the ground and excited state has been utilized to scrutinize the interaction phenomena. Differential modulation in the prototropic equilibrium of HM in the aforesaid aggregates has been explained on the basis of the structural dissimilarities of the bile salt monomers. The contrived hydrophobic surroundings provided by the aggregates have been reflected on the spectroscopic results, especially in the time-resolved fluorescence and the rotational dynamical behavior of the molecule of interest. Slow solvent reorientation time with regard to the lifetime of HM proliferated by the red-edge effect in two specific bile salts namely NaC and NaTC, whereas its absence in NaDC aggregates has also been elucidated on the basis of accessibility of the solvent molecules within the aggregates.

Stoppering/unstoppering of a rotaxane formed between an N-hetorycle ligand containing surfactant: β-cyclodextrin pseudorotaxane and pentacyanoferrate(II) ions

The assembly of a surfactant-based rotaxane by adding the labile aquopentacyanoferrate(II) ion to the previously formed pseudorotaxane between the surfactant 11-(isonicotinoyloxy)-N,N,N-triethyl-1-undecanaminium bromide and β-cyclodextrin was investigated by ¹H NMR and kinetic measurements. NMR spectroscopy has showed that the rotaxane can be formed through two different mechanisms. The rotaxane can be unstoppered by using the pyridine ligand substitution reaction by the high-field cyanide ligand. In this work a new method is developed for the preparation of several new surfactant-based rotaxanes by changing the hydrophilic and hydrophobic regions of the surfactants and the nature of the macrocycle.

pH responsive vesicles with tunable size formed by single-tailed surfactants with a dendritic headgroup

Vesicles of variable sizes are obtained by changing pH with single-tailed dendritic surfactants.

Acridone in a biological nanocavity: detailed spectroscopic and docking analyses of probing both the tryptophan residues of bovine serum albumin

AD initially gets hooked to Trp 212 housed in domain IIA, inducing conformational changes in the protein and paving the way for the ligand to reach Trp 134 located in domain IB.