Bile salts as biological surfactants

Interfacial behaviour of human bile and its substitution for in vitro lipolysis studies

This study examined the interfacial evolution of individual bile salts (BSs) and their blends with phosphatidylcholine (BS/PC) to simulate the complex behaviour of human bile (HB) during lipolysis at the triglyceride/water interface. Using adsorption and desorption cycles, mimicking exposure to small intestinal fluids, we demonstrate that the interfacial behaviour of real HB can be replicated using simple mixtures of BSs and PC. Interfacial tension (IFT) measurements after lipolysis and desorption showed no significant differences (P > 0.05) between HB samples and BS/PC mixtures across the total BS concentrations analysed (2.23-7.81 mM). However, individual BSs without PC yielded significantly different IFT results (P < 0.01) compared to HB, highlighting the importance of phospholipids. Dilatation rheology further emphasised the need for accurate phospholipid representation in bile models. Our results suggest that phospholipids in HB and in BS/PC systems enhance resistance to desorption, potentially affecting lipolysis. This is important, as current in vitro digestion models often replicate only intestinal BS concentrations to mimic the behaviour of HB in the intestinal lumen. Furthermore, the specific composition of BSs in HB appears less critical than the overall BS and phospholipid contents, suggesting that the kinetics of triglyceride digestion is influenced by the combined luminal concentrations of these components. These findings have significant implications for understanding the role of bile in digestion and offer insights for designing more accurate in vitro models to study the gastrointestinal behaviour of food emulsions and lipid-based delivery systems.

Liraglutide and Colesevelam Change Serum and Fecal Bile Acid Levels in a Randomized Trial With Patients With Bile Acid Diarrhea

INTRODUCTION

Both liraglutide and colesevelam improve bile acid diarrhea symptoms. Colesevelam binds excess amounts of diarrhea-causing bile acids in the colon, whereas the mode of action for liraglutide remains elusive. In this article, we examined the impact of colesevelam and liraglutide treatment on the concentrations of bile acids in serum and feces and the fecal microbiota composition to better understand the 2 drugs' modes of action.

METHODS

Bile acid species were analyzed in serum and fecal samples from a randomized, double-blind, double-dummy trial at baseline and after 3 and 6 weeks of orally administered colesevelam (1,875 mg twice daily, n = 26) or subcutaneously administered liraglutide (uptitrated by weekly increments of 0.6 mg from 0.6 to 1.8 mg daily, n = 26) in patients with 75 selenium-homotaurocholic acid test-verified, idiopathic, or postcholecystectomy bile acid diarrhea. Fecal microbiota composition was analyzed by 16S rRNA gene amplicon sequencing at the same time points.

RESULTS

Colesevelam increased the fecal concentrations of all bile acid species, whereas it decreased serum concentrations of secondary bile acids. Liraglutide induced a small increase in serum unconjugated bile acid concentrations without affecting fecal bile acid concentrations. No changes in fecal microbiota composition were observed with either treatment.

DISCUSSION

Colesevelam and liraglutide exhibit distinct effects on serum and fecal bile acid concentrations with colesevelam reducing serum concentrations of secondary bile acids and promoting fecal bile acid excretion, whereas liraglutide enhances serum concentrations of unconjugated bile acids, potentially through deceleration of small intestinal transit time allowing more time for passive absorption of bile acids.

Bile Acid Diarrhea Is Associated With an Increased Incidence of Gastrointestinal Cancers

INTRODUCTION

Bile acid diarrhea (BAD) is an underrecognized and socially debilitating disease caused by high concentrations of bile acids in the colon. Bile acids directly and indirectly promote carcinogenesis. In this article, we investigated whether individuals with BAD have an increased risk of gastrointestinal (GI) cancers.

METHODS

By using the Danish health registries, adult individuals with BAD were identified by International Classification of Diseases 10th revision code K90.8 or referral to the diagnostic ⁷⁵selenium-homotaurocholic acid test followed by prescription of a bile acid sequestrant within 365 days (n = 5,245). Age- and sex-matched individuals without BAD were included for comparison (n = 52,450). We analyzed the cumulative incidence of GI cancers after BAD diagnosis and the odds ratios (ORs) of GI cancer 8 and 15 years before BAD diagnosis/matching.

RESULTS

Cumulative incidence of GI cancer 6 years after BAD diagnosis/matching was 1.6% in the BAD group and 1.1% in controls ( P = 0.01). The ORs of total GI cancer 8 and 15 years before BAD diagnosis were 6.16 (5.08-7.48) and 5.19 (4.28-6.29), respectively. Furthermore, 47 individuals with BAD (0.9%) and 250 (0.5%) controls died of GI cancer.

DISCUSSION

This nationwide cohort study indicates an association between BAD and GI cancers. We found both a higher incidence of GI cancer after BAD diagnosis compared with controls and increased OR of GI cancer before BAD diagnosis. Bearing in mind the underdiagnosis of BAD, the delay of BAD diagnosis, and the carcinogenic effect of bile acids, these findings warrant further investigations of the risk of GI cancer in individuals with BAD.

Critical aspects in dissolution testing of nanomaterials in the oro-gastrointestinal tract: the relevance of juice composition for hazard identification and grouping

The dissolution of a nanomaterial (NM) in an in vitro simulant of the oro-gastrointestinal (OGI) tract is an important predictor of its biodurability in vivo. The cascade addition of simulated digestive juices (saliva, stomach and intestine), including inorganic/organic biomacromolecules and digestive enzymes (complete composition, referred to as "Type 1 formulation"), strives for realistic representation of chemical composition of the OGI tract. However, the data robustness requires consideration of analytical feasibility, such as the use of simplified media. Here we present a systematic analysis of the effects exerted by different digestive juice formulations on the dissolution% (or half-life values) of benchmark NMs (e.g., zinc oxide, titanium dioxide, barium sulfate, and silicon dioxide). The digestive juices were progressively simplified by removal of components such as organic molecules, enzymes, and inorganic molecules (Type 2, 3 and 4). The results indicate that the "Type 1 formulation" augments the dissolution via sequestration of ions by measurable factors compared to formulations without enzymes (i.e., Type 3 and 4). Type 1 formulation is thus regarded as a preferable option for predicting NM biodurability for hazard assessment. However, for grouping purposes, the relative similarity among diverse nanoforms (NFs) of a NM is decisive. Two similarity algorithms were applied, and additional case studies comprising NFs and non NFs of the same substance were included. The results support the grouping decision by simplified formulation (Type 3) as a robust method for screening and grouping purposes.

Apple juice relieves loperamide-induced constipation in rats by downregulating the intestinal apical sodium-dependent bile acid transporter ASBT

Apples are known to exhibit various beneficial effects on human health. In the present study, we investigated the effect of continuous intake of apple juice (AJ) on constipation status. A single dose of loperamide in rats as the constipation model markedly decreased the weight and number of fecal pellets compared to saline-administered rats as a control. After the administration of AJ twice a day for seven days, recovery of defecation close to that of the control was observed in loperamide-treated rats. In addition, the total bile acid content in the feces increased from day 4 after the administration of AJ. Among hepatic and intestinal transporters and enzymes that regulate bile acids, the mRNA expression of the apical sodium-dependent bile acid transporter (Asbt, slc10a2) was decreased by AJ in rats. Furthermore, the Asbt-mediated bile acid transport activity in the rat ileum decreased after AJ administration. Moreover, in human colonic cancer-derived Caco-2 cells, AJ exposure for 24 and 48 h decreased the expressions of ASBT mRNA and protein, and the uptake activity of taurocholic acid in both 7- and 21-d cultures. Several components of AJ, such as procyanidins, decreased the expression of ASBT in Caco-2 cells. In conclusion, ASBT downregulation is a possible mechanism responsible for the constipation-relieving effect of apples, and procyanidins may play a role in downregulating ASBT, which leads to the beneficial effects of apples against constipation. Although it is generally agreed that the common dietary compositions play a role in constipation relief, the novel specific mechanism of apples found in this study would facilitate understanding food functions.

The role of bile acids in carcinogenesis

Bile acids are soluble derivatives of cholesterol produced in the liver that subsequently undergo bacterial transformation yielding a diverse array of metabolites. The bulk of bile acid synthesis takes place in the liver yielding primary bile acids; however, other tissues have also the capacity to generate bile acids (e.g. ovaries). Hepatic bile acids are then transported to bile and are subsequently released into the intestines. In the large intestine, a fraction of primary bile acids is converted to secondary bile acids by gut bacteria. The majority of the intestinal bile acids undergo reuptake and return to the liver. A small fraction of secondary and primary bile acids remains in the circulation and exert receptor-mediated and pure chemical effects (e.g. acidic bile in oesophageal cancer) on cancer cells. In this review, we assess how changes to bile acid biosynthesis, bile acid flux and local bile acid concentration modulate the behavior of different cancers. Here, we present in-depth the involvement of bile acids in oesophageal, gastric, hepatocellular, pancreatic, colorectal, breast, prostate, ovarian cancer. Previous studies often used bile acids in supraphysiological concentration, sometimes in concentrations 1000 times higher than the highest reported tissue or serum concentrations likely eliciting unspecific effects, a practice that we advocate against in this review. Furthermore, we show that, although bile acids were classically considered as pro-carcinogenic agents (e.g. oesophageal cancer), the dogma that switch, as lower concentrations of bile acids that correspond to their serum or tissue reference concentration possess anticancer activity in a subset of cancers. Differences in the response of cancers to bile acids lie in the differential expression of bile acid receptors between cancers (e.g. FXR vs. TGR5). UDCA, a bile acid that is sold as a generic medication against cholestasis or biliary surge, and its conjugates were identified with almost purely anticancer features suggesting a possibility for drug repurposing. Taken together, bile acids were considered as tumor inducers or tumor promoter molecules; nevertheless, in certain cancers, like breast cancer, bile acids in their reference concentrations may act as tumor suppressors suggesting a Janus-faced nature of bile acids in carcinogenesis.

Hemolytic Response of Iron Oxide Magnetic Nanoparticles at the Interface and in Bulk: Extraction of Blood Cells by Magnetic Nanoparticles

Surface-active and water-soluble magnetic nanoparticles (NPs) were synthesized in the presence of a series of amphiphilic molecules of different functional groups to determine the hemolytic response and their ability to extract blood cells across the interface and aqueous bulk while maintaining minimum hemolysis. Amphiphilic molecules such as Gemini surfactants of strong hydrophobicity and low hydrophilic-lipophilic balance produced surface-active magnetic NPs, which were highly cytotoxic even when placed at the blood suspension (aqueous)-air interface. A similar behavior was shown by water-soluble magnetic NPs produced using monomeric ionic and nonionic surfactants and different amino acids. The NPs produced using mild biological surfactants and mono- and oligosaccharides of the same functional group proved to be excellent blood cell extractors with minimum hemolysis. α/β-cyclodextrin and dextrose-stabilized magnetic NPs induced negligible hemolysis and extracted more than 50% of blood cells. The results showed that nontoxic magnetic NPs are excellent blood cell extractors from the blood suspension when tagged with amphiphilic molecules possessing good biocompatibility with cell membranes without inducing hemolysis. The work highlights the biological applicability of nontoxic magnetic NPs at biointerfaces and in blood suspensions.

Surfactant-based therapy against COVID-19: A review

The coronavirus disease 2019 (COVID-19) has led to serious health and economic damage to all over the world, and it still remains unstoppable. The SARS-CoV-2, by using its S-glycoprotein, binds with an angiotensin-converting enzyme 2 receptor, mostly present in alveolar epithelial type II cells. Eventually pulmonary surfactant depletion occurs. The pulmonary surfactant is necessary for maintaining the natural immunity as well as the surface tension reduction within the lung alveoli during the expiration. Its insufficiency results in the reduction of blood oxygenation, poor pulmonary regeneration, lung fibrosis, and finally the respiratory system collapses. Exogenous surfactants have previously shown great promise in the treatment of infant respiratory distress syndrome, and they may also aid in the healing of damaged alveolar cells and the prevention of respiratory failure. Surfactant based therapy has been advised for the prevention of COVID-19, and the trials have begun around the world. Furthermore, greater research on the timing, dose, and the distribution of surfactant to the COVID-19 patients is required before this technique can be implemented in clinical practice.

Physiology and Physical Chemistry of Bile Acids

Bile acids (BAs) are facial amphiphiles synthesized in the body of all vertebrates. They undergo the enterohepatic circulation: they are produced in the liver, stored in the gallbladder, released in the intestine, taken into the bloodstream and lastly re-absorbed in the liver. During this pathway, BAs are modified in their molecular structure by the action of enzymes and bacteria. Such transformations allow them to acquire the chemical-physical properties needed for fulling several activities including metabolic regulation, antimicrobial functions and solubilization of lipids in digestion. The versatility of BAs in the physiological functions has inspired their use in many bio-applications, making them important tools for active molecule delivery, metabolic disease treatments and emulsification processes in food and drug industries. Moreover, moving over the borders of the biological field, BAs have been largely investigated as building blocks for the construction of supramolecular aggregates having peculiar structural, mechanical, chemical and optical properties. The review starts with a biological analysis of the BAs functions before progressively switching to a general overview of BAs in pharmacology and medicine applications. Lastly the focus moves to the BAs use in material science.

Deciphering Human Microbiota-Host Chemical Interactions

Our gut harbors more microbes than any other body site, and accumulating evidence suggests that these organisms have a sizable impact on human health. Though efforts to classify the metabolic activities that define this microbial community have transformed the way we think about health and disease, our knowledge of gut microbially produced small molecules and their effects on host biology remains in its infancy. This Outlook surveys a range of approaches, hurdles, and advances in defining the chemical repertoire of the gut microbiota, drawing on examples with particularly strong links to human health. Progress toward understanding and manipulating this chemical language is being made with diverse chemical and biological expertise and could hold the key for combatting certain human diseases.

A Novel Fluorescence-Based Method to Evaluate Ileal Apical Sodium-Dependent Bile Acid Transporter ASBT

This study aimed to demonstrate usefulness of the fluorophore-labeled bile acid derivative, N-(24-[7-(4-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole)]amino-3α,7α,12α-trihydroxy-27-nor-5β-cholestan-26-oyl)-2'-aminoethane sulfonate (tauro-nor-THCA-24-DBD) as a substrate of apical sodium-dependent bile acid transporter (ASBT, SLC10A2), which is expressed at distal ileum for reabsorption of bile acids and to find a novel fluorescence-based method to evaluate ASBT activity. In HPLC analysis, chromatogram of tauro-nor-THCA-24-DBD showed double peaks: R- and S-isomers of the compound. When ASBT was expressed in Xenopus laevis oocytes, their uptakes were higher than those by control oocytes, demonstrating both are transported by ASBT. Therefore, results were analyzed separately as peak 1, peak 2 and sum of them. Concentration dependent uptake of tauro-nor-THCA-24-DBD in ASBT-expressing oocytes was saturable with Km 122 μM and Vmax 1.49 pmol/oocyte/30 min for peak 1, 30.7 μM and 1.34 pmol/oocyte/30 min for peak 2, and 40.6 μM and 2.36 pmol/oocyte/30 min for sum, respectively. These uptakes were decreased in the presence of taurocholic acid and in the Na⁺ free condition. Furthermore, in Caco-2 cells, tauro-nor-THCA-24-DBD uptake was also Na⁺-dependent and saturable. Additionally, these uptakes were decreased by elobixibat, a selective ASBT inhibitor. Accordingly, it was concluded that tauro-nor-THCA-24-DBD is a substrate of ASBT and useful to evaluate the intestinal ASBT transport activity.

Morphology of bile salts micelles and mixed micelles with lipolysis products, from scattering techniques and atomistic simulations

HYPOTHESES

Bile salts (BS) are biosurfactants released into the small intestine, which play key and contrasting roles in lipid digestion: they adsorb at interfaces and promote the adsorption of digestive enzymes onto fat droplets, while they also remove lipolysis products from that interface, solubilising them into mixed micelles. Small architectural variations on their chemical structure, specifically their bile acid moiety, are hypothesised to underlie these conflicting functionalities, which should be reflected in different aggregation and solubilisation behaviour.

EXPERIMENTS

The micellisation of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ by one hydroxyl group on the bile acid moiety, was assessed by pyrene fluorescence spectroscopy, and the morphology of aggregates formed in the absence and presence of fatty acids (FA) and monoacylglycerols (MAG) - typical lipolysis products - was resolved by small-angle X-ray/neutron scattering (SAXS, SANS) and molecular dynamics simulations. The solubilisation by BS of triacylglycerol-incorporating liposomes - mimicking ingested lipids - was studied by neutron reflectometry and SANS.

FINDINGS

Our results demonstrate that BS micelles exhibit an ellipsoidal shape. NaTDC displays a lower critical micellar concentration and forms larger and more spherical aggregates than NaTC. Similar observations were made for BS micelles mixed with FA and MAG. Structural studies with liposomes show that the addition of BS induces their solubilisation into mixed micelles, with NaTDC displaying a higher solubilising capacity.

Surfactant-based prophylaxis and therapy against COVID-19: A possibility

Hand hygiene by washing with soap and water is recommended for the prevention of COVID-19 spread. Soaps and detergents are explained to act by damaging viral spike glycoproteins (peplomers) or by washing out the virus through entrapment in the micelles. Technically, soaps come under a functional category of molecules known as surfactants. Surfactants are widely used in pharmaceutical formulations as excipients. We wonder why surfactants are still not tried for prophylaxis or therapy against COVID-19? That too when many of them have proven antiviral properties. Moreover, lung surfactants have already shown benefits in respiratory viral infections. Therefore, we postulate that surfactant-based prophylaxis and therapy would be promising. We believe that our hypothesis would stimulate debate or new research exploring the possibility of surfactant-based prophylaxis and therapy against COVID-19. The success of a surfactant-based technique would save the world from any such pandemic in the future too.

Association between 12α-hydroxylated bile acids and hepatic steatosis in rats fed a high-fat diet

High-fat (HF) diet induces hepatic steatosis that is a risk factor for noncommunicable diseases such as obesity, type 2 diabetes and cardiovascular disease. Previously, we found that HF feeding in rats increases the excretion of fecal bile acids (BAs), specifically 12α-hydroxylated (12αOH) BAs. Although the liver is the metabolic center in our body, the association between hepatic steatosis and 12αOH BAs in HF-fed rats is unclear. Thus, we investigated extensively BA composition in HF-fed rats and evaluated the association between hepatic steatosis and 12αOH BAs. Acclimated male inbred WKAH/HkmSlc rats were divided into two groups and fed either control or HF diet for 8 weeks. Feeding HF diet increased hepatic triglyceride and total cholesterol concentrations, which correlated positively with 12αOH BAs concentrations but not with non-12αOH BAs in the feces, portal plasma and liver. Accompanied by the increase in 12αOH BAs, the rats fed HF diet showed increased fat absorption and higher mRNA expression of liver Cidea. The enhancement of 12αOH BA secretion may contribute to hepatic steatosis by the promotion of dietary fat absorption and hepatic Cidea mRNA expression. The increase in 12αOH BAs was associated with enhanced liver cholesterol 7α-hydroxylase (Cyp7a1) and sterol 12α-hydroxylase (Cyp8b1) mRNA expression. There was a significant increase in 7α-hydroxycholesterol, a precursor of BAs, in the liver of HF-fed rats. Altogether, these data suggest that the HF diet increases preferentially 12αOH BAs synthesis by utilizing the accumulated hepatic cholesterol and enhancing mRNA expression of Cyp7a1 and Cyp8b1 in the liver.

Interactions of bile salts with a dietary fibre, methylcellulose, and impact on lipolysis

Methylcellulose (MC) has a demonstrated capacity to reduce fat absorption, hypothetically through bile salt (BS) activity inhibition. We investigated MC cholesterol-lowering mechanism, and compared the influence of two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), which differ slightly by their architecture and exhibit contrasting functions during lipolysis. BS/MC bulk interactions were investigated by rheology, and BS behaviour at the MC/water interface studied with surface pressure and ellipsometry measurements. In vitro lipolysis studies were performed to evaluate the effect of BS on MC-stabilised emulsion droplets microstructure, with confocal microscopy, and free fatty acids release, with the pH-stat method. Our results demonstrate that BS structure dictates their interactions with MC, which, in turn, impact lipolysis. Compared to NaTC, NaTDC alters MC viscoelasticity more significantly, which may correlate with its weaker ability to promote lipolysis, and desorbs from the interface at lower concentrations, which may explain its higher propensity to destabilise emulsions.

Intestinal Absorption of Bile Acids in Health and Disease

The intestinal reclamation of bile acids is crucial for the maintenance of their enterohepatic circulation. The majority of bile acids are actively absorbed via specific transport proteins that are highly expressed in the distal ileum. The uptake of bile acids by intestinal epithelial cells modulates the activation of cytosolic and membrane receptors such as the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (GPBAR1), which has a profound effect on hepatic synthesis of bile acids as well as glucose and lipid metabolism. Extensive research has focused on delineating the processes of bile acid absorption and determining the contribution of dysregulated ileal signaling in the development of intestinal and hepatic disorders. For example, a decrease in the levels of the bile acid-induced ileal hormone FGF15/19 is implicated in bile acid-induced diarrhea (BAD). Conversely, the increase in bile acid absorption with subsequent overload of bile acids could be involved in the pathophysiology of liver and metabolic disorders such as fatty liver diseases and type 2 diabetes mellitus. This review article will attempt to provide a comprehensive overview of the mechanisms involved in the intestinal handling of bile acids, the pathological implications of disrupted intestinal bile acid homeostasis, and the potential therapeutic targets for the treatment of bile acid-related disorders. Published 2020. Compr Physiol 10:21-56, 2020.

Interplay of Supersaturation and Solubilization: Lack of Correlation between Concentration-Based Supersaturation Measurements and Membrane Transport Rates in Simulated and Aspirated Human Fluids

Supersaturating formulations are increasingly being used to improve the absorption of orally administered poorly water-soluble drugs. To better predict outcomes in vivo, we must be able to accurately determine the degree of supersaturation in complex media designed to provide a surrogate for the gastrointestinal environment. Herein, we demonstrate that relying on measurements based on consideration of the total dissolved concentration leads to underestimation of supersaturation and consequently membrane transport rates. Crystalline and amorphous solubilities of two compounds, atazanavir and posaconazole, were evaluated in six different media. Concurrently, diffusive flux measurements were performed in a side-by-side diffusion cell to determine the activity-based supersaturation by evaluating membrane transport rates at the crystalline and amorphous solubilities. Solubility values were found to vary in each medium because of different solubilization capacities. Concentration-based supersaturation ratios were also found to vary for the different media. Activity-based measurements, however, were largely independent of the medium, leading to relatively constant values for the estimated supersaturation. These findings have important consequences for modeling and prediction of supersaturation impact on the absorption rate as well as for better defining the thermodynamic driving force for crystallization in complex media.

Molecular insights into the behaviour of bile salts at interfaces: a key to their role in lipid digestion

HYPOTHESES

Understanding the mechanisms underlying lipolysis is crucial to address the ongoing obesity crisis and associated cardiometabolic disorders. Bile salts (BS), biosurfactants present in the small intestine, play key roles in lipid digestion and absorption. It is hypothesised that their contrasting functionalities - adsorption at oil/water interfaces and shuttling of lipolysis products away from these interfaces - are linked to their structural diversity. We investigate the interfacial films formed by two BS, sodium taurocholate (NaTC) and sodium taurodeoxycholate (NaTDC), differing by the presence or absence of a hydroxyl group on their steroid skeleton.

EXPERIMENTS

Their adsorption behaviour at the air/water interface and interaction with a phospholipid monolayer - used to mimic a fat droplet interface - were assessed by surface pressure measurements and ellipsometry, while interfacial morphologies were characterised in the lateral and perpendicular directions by Brewster angle microscopy, X-ray and neutron reflectometry, and molecular dynamics simulations.

FINDINGS

Our results provide a comprehensive molecular-level understanding of the mechanisms governing BS interfacial behaviour. NaTC shows a higher affinity for the air/water and lipid/water interfaces, and may therefore favour enzyme adsorption, whereas NaTDC exhibits a higher propensity for desorption from these interfaces, and may thus more effectively displace hydrolysis products from the interface, through dynamic exchange.

Block copolymers as bile salt sequestrants: intriguing structures formed in a mixture of an oppositely charged amphiphilic block copolymer and bile salt

To study the formation and characterize the structure of mixed complexes of oppositely charged block copolymers and surfactants are of great significance for practical applications, e.g., in drug carrier formulations that are based on electrostatically assisted assembly. In this context, biocompatible block copolymers and biosurfactants (like bile salts) are particularly interesting. In this work, we report on the co-assembly in dilute aqueous solution between a cationic poly(N-isopropyl acryl amide) (PNIPAM) diblock copolymer and the oppositely charged bile salt surfactant sodium deoxycholate at ambient temperature. The cryogenic transmission electron microscopy (cryo-TEM) experiments revealed the co-existence of two types of co-assembled complexes of radically different morphology and inner structure. They are formed mainly as a result of the electrostatic attraction between the positively charged copolymer blocks and bile salt anions and highlight the potential of using linear amphiphilic block copolymers as bile salt sequestrants in the treatment of bile acid malabsorption and hypercholesterolemia. The first complex of globular morphology has a coacervate core of deoxycholate anions and charged copolymer blocks surrounded by a PNIPAM corona. The second complex has an intriguing tape-like supramolecular morphology of several micrometer in length that is striped in the direction of the long axis. A model is presented in which the stretched cationic blocks of several block copolymers interact electrostatically with the bile salt molecules that are associated to form a zipper-like structure. The tape is covered on both sides by the PNIPAM chains that stabilize the overall complex in solution. In addition to cryo-TEM, the mixed system was investigated in a range of molar charge fractions at a constant copolymer concentration by static light scattering, small angle X-ray scattering, and electrophoretic mobility measurements.

The 7α-hydroxysteroid dehydratase Hsh2 is essential for anaerobic degradation of the steroid skeleton of 7α-hydroxyl bile salts in the novel denitrifying bacterium Azoarcus sp. strain Aa7

Bile salts are steroid compounds from the digestive tract of vertebrates and enter the environment via defecation. Many aerobic bile-salt degrading bacteria are known but no bacteria that completely degrade bile salts under anoxic conditions have been isolated so far. In this study, the facultatively anaerobic Betaproteobacterium Azoarcus sp. strain Aa7 was isolated that grew with bile salts as sole carbon source under anoxic conditions with nitrate as electron acceptor. Phenotypic and genomic characterization revealed that strain Aa7 used the 2,3-seco pathway for the degradation of bile salts as found in other denitrifying steroid-degrading bacteria such as Sterolibacterium denitrificans. Under oxic conditions strain Aa7 used the 9,10-seco pathway as found in, for example, Pseudomonas stutzeri Chol1. Metabolite analysis during anaerobic growth indicated a reductive dehydroxylation of 7α-hydroxyl bile salts. Deletion of the gene hsh2 _Aa7 encoding a 7-hydroxysteroid dehydratase led to strongly impaired growth with cholate and chenodeoxycholate but not with deoxycholate lacking a hydroxyl group at C7. The hsh2 _Aa7 deletion mutant degraded cholate and chenodeoxycholate to the corresponding C₁₉ -androstadienediones only while no phenotype change was observed during aerobic degradation of cholate. These results showed that removal of the 7α-hydroxyl group was essential for cleavage of the steroid skeleton under anoxic conditions.

Genome Sequence of the Bile Salt-Degrading Bacterium Novosphingobium sp. Strain Chol11, a Model Organism for Bacterial Steroid Catabolism

Many bacteria from different phylogenetic groups are able to degrade eukaryotic steroid compounds, but the underlying metabolic pathways are still not well understood. Novosphingobium sp. strain Chol11 is a steroid-degrading alphaproteobacterium. Its genome sequence reveals that it lacks several genes for steroid degradation known to exist in other model organisms.

Different approaches to heart valve decellularization: A comprehensive overview of the past 30 years

Xenogeneic decellularized heart valve scaffolds have the potential to overcome the limitations of existing bioprosthetic heart valves that have limited duration due to calcification and tissue degeneration phenomena. This article presents a review of 30 years of decellularization approaches adopted in cardiovascular tissue engineering, with a focus on the use, either individually or in combination, of different detergents. The safety and efficacy of cell-removal procedures are specifically reported and discussed, as well as the structure and biomechanics of the treated extracellular matrix (ECM). Detergent residues within the ECM, production of hyaluronan fragments, safe removal of cellular debris, and the persistence of the alpha-Gal epitope after the decellularization treatments are of particular interest as parameters for the identification of the best tissue for the manufacture of bioprostheses. Special attention has also been given to key factors that should be considered in the manufacture of the next generation of xenogeneic bioprostheses, where tissues must retain the ability to be remodeled and to grow in weight along with body reshaping.

Quantitative profiling of 19 bile acids in rat plasma, liver, bile and different intestinal section contents to investigate bile acid homeostasis and the application of temporal variation of endogenous bile acids

Bile acid homeostasis is maintained by liver synthesis, bile duct secretion, microbial metabolism and intestinal reabsorption into the blood. When drug insults result in liver damage, the variances of bile acids (BAs) are related to the physiological status of the liver. Here, we established a method to simultaneously quantify 19 BAs in rat plasma, liver, bile and different intestinal section contents (duodenum, jejunum, ileum, cecum and colon) using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) to reveal the pattern of bile acid homeostasis in the enterohepatic circulation of bile acids in physiological situations. Dynamic changes in bile acid composition appeared throughout the enterohepatic circulation of the BAs; taurine- and glycine-conjugated BAs and free BAs had different dynamic homeostasis levels in the circulatory system. cholic acid (CA), beta-muricholic acid (beta-MCA), lithocholic acid (LCA), glycocholic acid (GCA) and taurocholic acid (TCA) greatly fluctuated in the bile acid pool under physiological conditions. Taurine- and glycine-conjugated bile acids constituted more than 90% in the bile and liver, whereas GCA and TCA accounted for more than half of the total bile acids and the secretion of bile mainly via conjugating with taurine. While over 80% of BAs in plasma were unconjugated bile acids, CA and HDCA were the most abundant elements. Unconjugated bile acids constituted more than 90% in the intestine, and CA, beta-MCA and HDCA were the top three bile acids in the duodenum, jejunum and ileum content, but LCA and HDCA were highest in the cecum and colon content. As the main secondary bile acid converted by microflora in the intestine, LCA was enriched in the cecum and DCA mostly in the colon. As endogenous substances, the concentrations of plasma BAs were closely related to time rhythm and diet. In conclusion, analyzing detailed BA profiles in the enterohepatic circulation of bile acids in a single run is possible using LC-MS/MS. Based on the physiological characteristics of the metabolic profiling of 19 BAs in the total bile acid pool and the time rhythm variation of the endogenous bile acids, this study provided a new valuable method and theoretical basis for the clinical research of bile acid homeostasis.

Compositional effect of complex biorelevant media on the crystallization kinetics of an active pharmaceutical ingredient

Bile salts impact crystal nucleation and growth of supersaturated solutions of poorly water soluble drugs.

Crystalline arrays of side chain modified bile acids derivatives. Two novel self-assemblies based on π-π and belly-to-belly interactions

Crystalline derivatives of side chain modified bile acids were efficiently prepared from the naturally occurring steroids by palladium-catalyzed cross coupling reaction as a key step. The solvent-free crystalline bile acids derivatives 2b-e are readily accessed by slow evaporation from selected solvents. A variety of steroidal scaffolds were found and elucidated by SXRD studies. The crystal packing of the title compounds are dominated by hydrogen-bonding interactions established between differently positioned acetyl protecting groups, which in the case of 2b and 2e take advantage of the facial amphiphilicity producing two novel steroidal supramolecular self-assemblies combining π-π and strong facial interactions. Thus, these crystalline arrays of side chain modified bile acids represent promising scaffolds for research and implementation in biomolecular materials or inclusion phenomena.

Interaction of Biologically Active Flavins inside Bile Salt Aggregates: Molecular Level Investigation

In this work we have studied the photophysics of biologically active flavin molecule lumichrome (LCM) in different bile-salt aggregates. With alteration of the functional groups of the bile salts, the photophysics of confined fluorophore is largely affected and shows difference in their spectral behavior. This study also reveals the selective prototropic species of LCM present in bile salt aggregates. In the presence of the bile salt aggregates, LCM molecule shows excitation and emission wavelength-dependent emission properties, indicating switch over of the structural change of different prototropic form of the LCM molecule. The observation of higher rotational relaxation time in NaDC aggregates compared to NaTC aggregates clearly reflects that NaDC aggregates are more rigid due to its greater hydrophobicity and large in size, which is capable to bind the guest molecule more into their nanoconfined medium. Moreover, due to less acidic nature, NaDC aggregates have more ability to accept hydrogen bond from the LCM molecule and show the selective formation of isoalloxazine N10 anion (A1 monoanionic form) of LCM.

Hydrogen bonding asymmetric star-shape derivative of bile acid leads to supramolecular fibrillar aggregates that wrap into micrometer spheres

We report that star-shaped molecules with cholic acid cores asymmetrically grafted by low molecular weight polymers with hydrogen bonding end-groups undergo aggregation to nanofibers, which subsequently wrap into micrometer spherical aggregates with low density cores. Therein the facially amphiphilic cholic acid (CA) is functionalized by four flexible allyl glycidyl ether (AGE) side chains, which are terminated with hydrogen bonding 2-ureido-4[1H]pyrimidinone (UPy) end-groups as connected by hexyl spacers, denoted as CA(AGE6-C6H12-UPy)4. This wedge-shaped molecule is expected to allow the formation of a rich variety of solvent-dependent structures due to the complex interplay of interactions, enabled by its polar/nonpolar surface-active structure, the hydrophobicity of the CA in aqueous medium, and the possibility to control hydrogen bonding between UPy molecules by solvent selection. In DMSO, the surfactant-like CA(AGE6-C6H12-UPy)4 self-assembles into nanometer scale micelles, as expected due to its nonpolar CA apexes, solubilized AGE6-C6H12-UPy chains, and suppressed mutual hydrogen bonds between the UPys. Dialysis in water leads to nanofibers with lateral dimensions of 20-50 nm. This is explained by promoted aggregation as the hydrogen bonds between UPy molecules start to become activated, the reduced solvent dispersibility of the AGE-chains, and the hydrophobicity of CA. Finally, in pure water the nanofibers wrap into micrometer spheres having low density cores. In this case, strong complementary hydrogen bonds between UPy molecules of different molecules can form, thus promoting lateral interactions between the nanofibers, as allowed by the hydrophobic hexyl spacers. The wrapping is illustrated by transmission electron microscopy tomographic 3D reconstructions. More generally, we foresee hierarchically structured matter bridging the length scales from molecular to micrometer scale by sequentially triggering supramolecular interactions.

Photoactive bile salts with critical micellar concentration in the micromolar range

The aggregation behavior of bile salts is strongly dependent on the number of hydroxyl groups.

Radical-mediated dehydrogenation of bile acids by means of hydrogen atom transfer to triplet carbonyls

The aim of the present paper is to explore the potential of radical-mediated dehydrogenation of bile salts (BSs), which is reminiscent of the enzymatic action of hydroxysteroid dehydrogenase enzymes (HSDH).

Interaction between bile salt sodium glycodeoxycholate and PEO–PPO–PEO triblock copolymers in aqueous solution

Bile salts can associate to PEO–PPO–PEO block copolymer micelles and disintegrate them depending on the relative block length and molecular weight of the copolymers and bile salt/copolymer molar ratio.

The mechanism of lowering cholesterol absorption by calcium studied by using an in vitro digestion model

Ca²⁺decreases strongly cholesterol and saturated fatty acid bioaccessibility duringin vitrolipid digestion, explaining the lowering of serum cholesterolin vivo.

Effects of Bile Salt Sodium Glycodeoxycholate on the Self-Assembly of PEO-PPO-PEO Triblock Copolymer P123 in Aqueous Solution

A comprehensive experimental study on the interaction between the PEO-PPO-PEO block copolymer P123 (EO20PO68EO20) and the anionic bile salt sodium glycodeoxycholate (NaGDC) in water has been performed. The work was aimed at investigating the suitability of using P123 as bile salt sequestrant beside the fundamental aspects of PEO-PPO-PEO block copolymer-bile salt interactions. Various experimental techniques including dynamic and static light scattering, small-angle X-ray scattering, and differential scanning calorimetry (DSC) were employed in combination with electrophoretic mobility measurements. The system was investigated at a constant P123 concentration of 1.74 mM and with varying bile salt concentrations up to approximately 250 mM NaGDC (or a molar ratio n(NaGDC)/n(P123) = 144). In the mixed P123-NaGDC solutions, the endothermic process related to the self-assembly of P123 was observed to gradually decrease in enthalpy and shift to higher temperatures upon progressive addition of NaGDC. To explain this effect, the formation of NaGDC micelles carrying partly dehydrated P123 unimers was proposed and translated into a stoichiometric model, which was able to fit the experimental DSC data. In the mixtures at low molar ratios, NaGDC monomers associated with the P123 micelle forming a charged "P123 micelle-NaGDC" complex with a dehydrated PPO core. These complexes disintegrated upon increasing NaGDC concentration to form small "NaGDC-P123" complexes visualized as bile salt micelles including one or a few P123 copolymer chains.

Oral delivery of zoledronic acid by non-covalent conjugation with lysine-deoxycholic acid: In vitro characterization and in vivo anti-osteoporotic efficacy in ovariectomized rats

We assessed the possibility of changing the route of administration of zoledronic acid to an oral dosage form and its therapeutic efficacy in an estrogen-deficient osteoporosis rat model. To enhance oral bioavailability, we formed an ionic complex by electrostatic conjugation of zoledronic acid with lysine-linked deoxycholic acid (Lys-DOCA, an oral absorption enhancer). After forming the complex, the characteristic crystalline features of pure zoledronic acid disappeared completely in the powder X-ray diffractogram and differential scanning calorimetry thermogram, indicating that zoledronic acid existed in an amorphous form in the complex. In vitro permeabilities of zoledronic acid/Lys-DOCA (1:1) (ZD1) and zoledronic acid/Lys-DOCA (1:2) (ZD2) complex across Caco-2 cell monolayers were 2.47- and 4.74-fold higher than that of zoledronic acid, respectively. Upon intra-jejunal administration to rats, the intestinal absorption of zoledronic acid was increased significantly and the resulting oral bioavailability of the ZD2 complex was determined to be 6.76±2.59% (0.548±0.161% for zoledronic acid). Ovariectomized (OVX) rats showed 122% increased bone mineral density versus the OVX control at 12weeks after treatment with once weekly oral administration of ZD2 complex (16μg/kg of zoledronic acid). Furthermore, rats treated with ZD2 complex orally showed significant improvement in the parameters of trabecular microarchitecture and bone strength: 149% higher bone volume fraction (BV/TV), 115% higher trabecular number (Tb.N), and 56% higher mean maximum load (Fmax) than in the OVX group. The trabecular microstructure and bone mechanical properties in the oral zoledronic acid group were not significantly changed compared with the OVX control. Thus, the oral ZD2 complex inhibited osteoporosis progression effectively by promoting osteogenesis and trabecular connectivity. The oral ZD2 complex would be expected to improve patient compliance by replacing the conventional injectable form and expand the indications, to include prophylaxis for osteoporosis and bone metastases.

Absorption-Enhancing Effects of Bile Salts

Bile salts are ionic amphiphilic compounds with a steroid skeleton. Among the most important physiological properties of bile salts are lipid transport by solubilization and transport of some drugs through hydrophobic barriers. Bile salts have been extensively studied to enhance transepithelial permeability for different marker molecules and drugs. They readily agglomerate at concentrations above their critical micelle concentration (CMC). The mechanism of absorption enhancement by bile salts appears to be complex. The aim of the present article was to review bile salt structure and their application as absorption enhancers and the probable mechanism for increasing permeation based on previous studies.

Quantification of 15 bile acids in lake charr feces by ultra-high performance liquid chromatography-tandem mass spectrometry

Many fishes are hypothesized to use bile acids (BAs) as chemical cues, yet quantification of BAs in biological samples and the required methods remain limited. Here, we present an UHPLC-MS/MS method for simultaneous, sensitive, and rapid quantification of 15 BAs, including free, taurine, and glycine conjugated BAs, and application of the method to fecal samples from lake charr (Salvelinus namaycush). The analytes were separated on a C18 column with acetonitrile-water (containing 7.5mM ammonium acetate and 0.1% formic acid) as mobile phase at a flow rate of 0.25mL/min for 12min. BAs were monitored with a negative electrospray triple quadrupole mass spectrometer (Xevo TQ-S™). Calibration curves of 15 BAs were linear over the concentration range of 1.00-5,000ng/mL. Validation revealed that the method was specific, accurate, and precise. The method was applied to quantitative analysis of feces extract of fry lake charr and the food they were eating. The concentrations of analytes CA, TCDCA, TCA, and CDCA were 242.3, 81.2, 60.7, and 36.2ng/mg, respectively. However, other taurine conjugated BAs, TUDCA, TDCA, and THDCA, were not detected in feces of lake charr. Interestingly, TCA and TCDCA were detected at high concentrations in food pellets, at 71.9 and 38.2ng/mg, respectively. Application of the method to feces samples from lake charr supported a role of BAs as chemical cues, and will enhance further investigation of BAs as chemical cues in other fish species.

Modulated photophysics of an anthracene-based fluorophore within bile-salt aggregates: the effect of the ionic strength of the medium on the aggregation behavior

Binding interactions of an anthracene-based fluorescent probe with a series of bile-salt aggregates of varying hydrophobicity, as well as salt induced alterations of the binding behavior have been thoroughly demonstrated.