Heuman indices of hydrophobicity of bile acids and their comparison with a newly developed and conventional molecular descriptors

Self-Association of the Anion of 7-Oxodeoxycholic Acid (Bile Salt): How Secondary Micelles Are Formed

Bile acid anions are steroidal biosurfactants that form primary micelles due to the hydrophobic effect. At higher concentrations of some bile acid anions, secondary micelles are formed; hydrogen bonds connect primary micelles. Monoketo derivatives of cholic acid, which have reduced membrane toxicity, are important for biopharmaceutical examinations. The main goal is to explain why the processes of formation of primary and secondary micelles are separated from each other, i.e., why secondary micelles do not form parallel to primary micelles. The association of the anion of 7-oxodeoxycholic acid (a monoketo derivative of cholic acid) is observed through the dependence of the spin-lattice relaxation time on total surfactant concentration T₁ = f(C_T). On the function T₁ = f(C_T), two sharp jumps of the spin-lattice relaxation time are obtained, i.e., two critical micellar concentrations (CMC). The aggregation number of the micelle at 50 mM total concentration of 7-oxodeoxycholic acid anions in the aqueous solution is 4.2 ± 0.3, while at the total concentration of 100 mM the aggregation number is 9.0 ± 0.9. The aggregation number of the micelle changes abruptly in the concentration interval of 80-90 mM (the aggregation number determined using fluorescence measurements). By applying Le Chatelier's principle, the new mechanism of formation of secondary micelles is given, and the decoupling of the process of formation of primary and secondary micelles at lower concentrations of monomers (around the first critical micellar concentration) and the coupling of the same processes at higher equilibrium concentrations of monomers (around the second critical micellar concentration) is explained. Stereochemically and thermodynamically, a direct mutual association of primary micelles is less likely, but monomeric units are more likely to be attached to primary micelles, i.e., 7-oxodeoxycholic acid anions.

Symmetry (Asymmetry) of the Molar Excess Gibbs Free Energy Function of the Binary Mixed Micelles of Bile Acid Anion and Classical Cationic Surfactant: Influence of Sterically Shielded and Sterically Unshielded Polar Groups of the Steroid Skeleton

Binary mixtures of surfactants build a binary mixed micelle in which the ratio of surfactants usually differs from the initial ratio of surfactants in their binary mixture. The thermodynamic stabilization of the binary mixed micellar pseudophase about the hypothetical ideal state (intermolecular interactions between the different particles and the conformational states of the particles are identical to those of monocomponent states) is described by the molar excess Gibbs free energy (gE). The dependence of gE on the molar fraction of surfactant i (xi) from the binary mixed micelle can be described by a symmetric function (symmetry is described to the line parallel to the y-axis and passes through xi = 0.5) or by an asymmetric function. Theoretical analysis (canonical partition function, conformational analysis) examines how the presence of different polar functional groups, some of which are sterically shielded from the steroid skeleton of bile salts (surfactant), affect the symmetry of the function gE of the binary mixed micelle of the cholic acid anion (bile salts) and classic cationic surfactant (hydrophobic tail and polar head). Suppose the steroid skeleton of the bile salt contains non-sterically shielded polar groups (or the temperature is relatively high). In that case, gE is a symmetric function. At the same time, if the steroid skeleton also contains sterically shielded polar groups, then the gE function is asymmetric.

On the mechanism of the cholesterol lowering ability of soluble dietary fibers: Interaction of some bile salts with pectin, alginate, and chitosan studied by isothermal titration calorimetry

Reducing high blood cholesterol is an important strategy to decrease the chances of a cardiovascular disease occurrence, the main cause of mortality in western developed countries. Therefore, the search for an alternative therapeutic or preventive approach being natural, biocompatible, and not toxic is still more relevant than ever. This need is particularly felt in Pediatrics for treating childhood hypercholesterolemia, due to statins interference in the production of steroid hormones in prepuberal children. Notwithstanding the general acceptance of the healthy role of the fibers in the diet, the mechanism underlying the cholesterol-lowering ability of soluble fibers is still under discussion. Therefore, we started a systematic study of the binding ability of some soluble dietary fibers (SDF) originated from different natural sources toward selected bile salts (BS) by isothermal titration calorimetry (ITC). Here we report the results of our ITC studies on the interaction of alginate, pectin and chitosan with sodium cholate (NaC), sodium deoxycholate (NaDC), sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC). Thermodynamic data on the micelle formation process of the above bile salts, as a premise to the study of their binding ability to the SDF, are also reported. Alginate does not show specific binding interaction with BS, while pectin shows a strong exothermic bond with NaDC in monomeric form. Chitosan, positively charged and soluble only at low pH, shows strong exothermic interactions with NaTC and NaTDC (soluble at pH = 3 in acetate buffer) with precipitate formation. For NaTC, the exothermic peak starts at about 5 mM. At this concentration NaTC bound on the fiber reaches locally the cmc value and micelles start forming on the fiber inducing its conformational change. For NaTDC the same process occurs at much lower concentrations, due to lower cmc, and with a greater quantity of heat involved. The first set of results here presented shows that for some SDF the binding of BS could be an important mechanism in cholesterol lowering but not the only one. The information here presented could be a starting point for the design of optimized functional foods with high cholesterol lowering ability.

Gypenosides Prevent and Dissolve Cholesterol Gallstones by Modulating the Homeostasis of Cholesterol and Bile Acids

Gypenosides (GPs), obtained from Gynostemma pentaphyllum (Thunb.) Makino, have been traditionally prescribed to treat metabolic disorders in Asians. This study assessed whether GPs could prevent lithogenic diet (LD)-induced cholesterol gallstone (CG) formation and enhance CG dissolution in mice. Gallstone-susceptible C57BL/6J mice were fed an LD or normal chow, with or without GPs. Bile acids (BAs) in gallbladder bile were analyzed by liquid chromatography-tandem mass spectrometry. Differentially expressed hepatic genes were identified by RNA sequencing, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. GPs were found to prevent LD-induced CG formation and to dissolve pre-existing LD-induced CGs. GPs reduced total cholesterol levels and increased BA levels in bile, as well as reducing the BA Hydrophobicity Index, ratio of 12α-hydroxylated (12α-OH) to non-12α-OH BAs, and Cholesterol Saturation Index in gallbladder bile. GO and KEGG pathway enrichment analyses indicated that GPs-induced genes were involved in BA biosynthesis and cholesterol metabolism. GPs increased the hepatic expression of genes encoding the cytochrome P450 (Cyp) enzymes Cyp7a1, Cyp7b1, and Cyp8b1, while decreasing the hepatic expression of genes encoding the adenosine triphosphate-binding cassette (Abc) transporters Abcg5 and Abcg8. GPs may be a promising strategy for preventing and dissolving CGs.

Interaction of Spike protein and lipid membrane of SARS-CoV-2 with Ursodeoxycholic acid, an in-silico analysis

Numerous repositioned drugs have been sought to decrease the severity of SARS-CoV-2 infection. It is known that among its physicochemical properties, Ursodeoxycholic Acid (UDCA) has a reduction in surface tension and cholesterol solubilization, it has also been used to treat cholesterol gallstones and viral hepatitis. In this study, molecular docking was performed with the SARS-CoV-2 Spike protein and UDCA. In order to confirm this interaction, we used Molecular Dynamics (MD) in “SARS-CoV-2 Spike protein-UDCA”. Using another system, we also simulated MD with six UDCA residues around the Spike protein at random, naming this “SARS-CoV-2 Spike protein-6UDCA”. Finally, we evaluated the possible interaction between UDCA and different types of membranes, considering the possible membrane conformation of SARS-CoV-2, this was named “SARS-CoV-2 membrane-UDCA”. In the “SARS-CoV-2 Spike protein-UDCA”, we found that UDCA exhibits affinity towards the central region of the Spike protein structure of − 386.35 kcal/mol, in a region with 3 alpha helices, which comprises residues from K986 to C1032 of each monomer. MD confirmed that UDCA remains attached and occasionally forms hydrogen bonds with residues R995 and T998. In the presence of UDCA, we observed that the distances between residues atoms OG1 and CG2 of T998 in the monomers A, B, and C in the prefusion state do not change and remain at 5.93 ± 0.62 and 7.78 ± 0.51 Å, respectively, compared to the post-fusion state. Next, in “SARS-CoV-2 Spike protein-6UDCA”, the three UDCA showed affinity towards different regions of the Spike protein, but only one of them remained bound to the region between the region's heptad repeat 1 and heptad repeat 2 (HR1 and HR2) for 375 ps of the trajectory. The RMSD of monomer C was the smallest of the three monomers with a value of 2.89 ± 0.32, likewise, the smallest RMSF was also of the monomer C (2.25 ± 056). In addition, in the simulation of “SARS-CoV-2 membrane-UDCA”, UDCA had a higher affinity toward the virion-like membrane; where three of the four residues remained attached once they were close (5 Å, to the centre of mass) to the membrane by 30 ns. However, only one of them remained attached to the plasma-like membrane and this was in a cluster of cholesterol molecules. We have shown that UDCA interacts in two distinct regions of Spike protein sequences. In addition, UDCA tends to stay bound to the membrane, which could potentially reduce the internalization of SARS-CoV-2 in the host cell.

The protective role of hydrophilic tetrahydroxylated bile acids (THBA)

Bile acids are key components of bile required for human health. In humans and mice, conditions of reduced bile flow, cholestasis, induce bile acid detoxification by producing tetrahydroxylated bile acids (THBA), more hydrophilic and less cytotoxic than the usual bile acids, which are typically di- or tri-hydroxylated. Mice deficient in the Bile Salt Export Pump (Bsep, or Abcb11), the primary bile acid transporter in liver cells, produce high levels of THBA, and avoid the severe liver damage typically seen in humans with BSEP deficiencies. THBA can suppress bile acid-induced liver damage in Mdr2-deficient mice, caused by their lack of phospholipids in bile exposing their biliary tracts to unbound bile acids. Here we review THBA-related works in both animals and humans, and discuss their potential relevance and applications as a class of functional bile acids.

Astragalus Polysaccharides Ameliorate Diet-Induced Gallstone Formation by Modulating Synthesis of Bile Acids and the Gut Microbiota

Cholesterol gallstone (CG) disease has relationships with several metabolic abnormalities. Astragalus polysaccharides (APS) have been shown to have multiple benefits against metabolic disorders. We attempted to uncover the effect and mechanism of action of APS on diet-induced CG formation in mice. Animals were fed a chow diet or lithogenic diet (LD) with or without APS supplementation. The effect of APS on CG formation was evaluated. The level of individual bile acids (BAs) in gallbladder bile and ileum were measured by liquid chromatography-tandem mass spectrometry. Real-time reverse transcription-quantitative polymerase chain reaction and western blotting were used to assess expression of the genes involved in BA metabolism and the enterohepatic circulation. Cecal contents were collected to characterize microbiota profiles. APS ameliorated LD-induced CG formation in mice. APS reduced the level of total cholesterol, bile acid hydrophobicity index and cholesterol saturation index in gallbladder bile. The protective effect of APS might result from reduced absorption of cholic acid in the intestine and increased hepatic BA synthesis. APS relieved the LD-induced activation of the intestinal farnesoid X receptor and decreased ileal expression of fibroblast growth factor 15. In the liver, expression of cytochrome P450 (Cyp) enzyme Cyp7a1 and Cyp7b1 was increased, whereas expression of adenosine triphosphate-binding cassette (Abc) transporters Abcg5 and Abcg8 was decreased by APS. APS improved the diversity of the gut microbiota and increased the relative abundance of the Bacteroidetes phylum. APS had demonstratable benefits against CG disease, which might be associated with enhanced BA synthesis and improved gut microbiota. Our results suggest that APS may be a potential strategy for the prevention of CG disease.

The Nonsteroidal Anti-Inflammatory Drug Ketorolac Alters the Small Intestinal Microbiota and Bile Acids Without Inducing Intestinal Damage or Delaying Peristalsis in the Rat

Background: Nonsteroidal anti-inflammatory drugs (NSAIDs) induce significant damage to the small intestine, which is accompanied by changes in intestinal bacteria (dysbiosis) and bile acids. However, it is still a question of debate whether besides mucosal inflammation also other factors, such as direct antibacterial effects or delayed peristalsis, contribute to NSAID-induced dysbiosis. Here we aimed to assess whether ketorolac, an NSAID lacking direct effects on gut bacteria, has any significant impact on intestinal microbiota and bile acids in the absence of mucosal inflammation. We also addressed the possibility that ketorolac-induced bacterial and bile acid alterations are due to a delay in gastrointestinal (GI) transit. Methods: Vehicle or ketorolac (1, 3 and 10 mg/kg) were given to rats by oral gavage once daily for four weeks, and the severity of mucosal inflammation was evaluated macroscopically, histologically, and by measuring the levels of inflammatory proteins and claudin-1 in the distal jejunal tissue. The luminal amount of bile acids was measured by liquid chromatography-tandem mass spectrometry, whereas the composition of microbiota by sequencing of bacterial 16S rRNA. GI transit was assessed by the charcoal meal method. Results: Ketorolac up to 3 mg/kg did not cause any signs of mucosal damage to the small intestine. However, 3 mg/kg of ketorolac induced dysbiosis, which was characterized by a loss of families belonging to Firmicutes (Paenibacillaceae, Clostridiales Family XIII, Christensenellaceae) and bloom of Enterobacteriaceae. Ketorolac also changed the composition of small intestinal bile by decreasing the concentration of conjugated bile acids and by increasing the amount of hyodeoxycholic acid (HDCA). The level of conjugated bile acids correlated negatively with the abundance of Erysipelotrichaceae, Ruminococcaceae, Clostridiaceae 1, Muribaculaceae, Bacteroidaceae, Burkholderiaceae and Bifidobacteriaceae. Ketorolac, under the present experimental conditions, did not change the GI transit. Conclusion: This is the first demonstration that low-dose ketorolac disturbed the delicate balance between small intestinal bacteria and bile acids, despite having no significant effect on intestinal mucosal integrity and peristalsis. Other, yet unidentified, factors may contribute to ketorolac-induced dysbiosis and bile dysmetabolism.

A comprehensive time course and correlation analysis of indomethacin-induced inflammation, bile acid alterations and dysbiosis in the rat small intestine

It has been proposed that changes in microbiota due to nonsteroidal anti-inflammatory drugs (NSAIDs) alter the composition of bile, and elevation of hydrophobic secondary bile acids contributes to small intestinal damage. However, little is known about the effect of NSAIDs on small intestinal bile acids, and whether bile alterations correlate with mucosal injury and dysbiosis. Here we determined the ileal bile acid metabolome and microbiota 24, 48 and 72 h after indomethacin treatment, and their correlation with each other and with tissue damage in rats. In parallel with the development of inflammation, indomethacin increased the ileal proportion of glycine and taurine conjugated bile acids, but not bile hydrophobicity. Firmicutes decreased with time, whereas Gammaproteobacteria increased first, but declined later and were partially replaced by Bilophila, Bacteroides and Fusobacterium. Mucosal injury correlated negatively with unconjugated bile acids and Gram-positive bacteria, and positively with taurine conjugates and some Gram-negative taxa. Strong positive correlation was found between Lactobacillaceae, Ruminococcaceae, Clostridiaceae and unconjugated bile acids. Indomethacin-induced dysbiosis was not likely due to direct antibacterial effects or alterations in luminal pH. Here we provide the first detailed characterization of indomethacin-induced time-dependent alterations in small intestinal bile acid composition, and their associations with mucosal injury and dysbiosis. Our results suggest that increased bile hydrophobicity is not likely to contribute to indomethacin-induced small intestinal damage.

Structure-Property Relationships in Sodium Muricholate Derivative (Bile Salts) Micellization: The Effect of Conformation of Steroid Skeleton on Hydrophobicity and Micelle Formation-Pattern Recognition and Potential Membranoprotective Properties

It is known that β-muricholic acid anions prevent membrane toxicity of hydrophobic bile acids, which are being used in therapy for solubilization of the cholesterol type bile stone. Better knowledge of these derivative micelles is very important for understanding their physiological and pharmacological effects. β-Axial (a) oriented hydroxyl group from the steroid skeleton decreases the hydrophobic surface of the convex side of the steroid skeleton. Therefore, the critical micellization concentration (CMC) for steroid surfactants with β-a-OH group should increase, but in the case of OH groups of different orientations forming H-bonds in the hydrophobic phase of the micelle, it has the opposite effect; the CMC decreses, and aggregation is more favored. The set of muricholic acids (MCs) is composed by α-MC, β-MC, γ-MC, and ω-MC, where α-MC and β-MC have β-axial-OH groups. The aggregation numbers (n) are determined using the Moroi-Matsuoka-Sugioka thermodynamic method. CMC, enthalpy of demicellization, and ΔC_p are determined by isothermal titration calorimetry (ITC). This report pioneers in the study of MC derivatives micellization. Micelles of β-MC and γ-MC belong to the linear congeneric group (LCG) and their micelles above 85 mM have constant aggregation numbers n = 4-5. Micelles of α-MC and ω-MC are outliers in relation to the LCG, their aggregation number constantly increases; at 85 mM n = 6.8 (α-MC) and 6.5 (ω-MC). In micelles of derivatives β-MC and γ-MC, there is a low probability for the existence of hydrogen bonds. A micelle of α-MC probably has hydrogen bonds in its hydrophobic domain.

Recent progresses in the exploration of machine learning methods as in-silico ADME prediction tools

In-silico methods have been explored as potential tools for assessing ADME and ADME regulatory properties particularly in early drug discovery stages. Machine learning methods, with their ability in classifying diverse structures and complex mechanisms, are well suited for predicting ADME and ADME regulatory properties. Recent efforts have been directed at the broadening of application scopes and the improvement of predictive performance with particular focuses on the coverage of ADME properties, and exploration of more diversified training data, appropriate molecular features, and consensus modeling. Moreover, several online machine learning ADME prediction servers have emerged. Here we review these progresses and discuss the performances, application prospects and challenges of exploring machine learning methods as useful tools in predicting ADME and ADME regulatory properties.

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.