Exploitation of bile acid transport systems in prodrug design

Liver-Targeted Delivery Based on Prodrug: Passive and Active Approaches

BACKGROUND

The liver, a central organ in human metabolism, is often the primary target for drugs. However, conditions such as viral hepatitis, cirrhosis, non-alcoholic fatty liver disease (NAFLD), and hepatocellular carcinoma (HCC) present substantial health challenges worldwide. Existing treatments, which suffer from the non-specific distribution of drugs, frequently fail to achieve desired efficacy and safety, risking unnecessary liver harm and systemic side effects.

PURPOSE

The aim of this review is to synthesize the latest progress in the design of liver-targeted prodrugs, with a focus on passive and active targeting strategies, providing new insights into the development of liver-targeted therapeutic approaches.

METHODS

This study conducted an extensive literature search through databases like Google Scholar, PubMed, Web of Science, and China National Knowledge Infrastructure (CNKI), systematically collecting and selecting recent research on liver-targeted prodrugs. The focus was on targeting mechanisms, including the Enhanced Permeability and Retention (EPR) effect, the unique microenvironment of liver cancer, and active targeting through specific transporters and receptors.

RESULTS

Active targeting strategies achieve precise drug delivery by binding specific ligands to liver surface receptors. Passive targeting takes advantage of the EPR effect and tumor characteristics to enrich drugs in liver tumors. The review details successful cases of using small molecule ligands, peptides, antibodies and nanoparticles as drug carriers.

CONCLUSION

Liver-targeted prodrug strategies show great potential in enhancing the efficacy of drug treatment and reducing side effects for liver diseases. Future research should balance the advantages and limitations of both targeting strategies, focusing on optimizing drug design and targeting efficiency, especially for clinical application. In-depth research on liver-specific receptors and the development of innovative targeting molecules are crucial for advancing the field of liver-targeted prodrugs.

Assessing causal associations of bile acids with obesity indicators: A Mendelian randomization study

Maintaining a balanced bile acids (BAs) metabolism is essential for lipid and cholesterol metabolism, as well as fat intake and absorption. The development of obesity may be intricately linked to BAs and their conjugated compounds. Our study aims to assess how BAs influence the obesity indicators by Mendelian randomization (MR) analysis. Instrumental variables of 5 BAs were obtained from public genome-wide association study databases, and 8 genome-wide association studies related to obesity indicators were used as outcomes. Causal inference analysis utilized inverse-variance weighted (IVW), weighted median, and MR-Egger methods. Sensitivity analysis involved MR-PRESSO and leave-one-out techniques to detect pleiotropy and outliers. Horizontal pleiotropy and heterogeneity were assessed using the MR-Egger intercept and Cochran Q statistic, respectively. The IVW analysis revealed an odds ratio of 0.94 (95% confidence interval: 0.88, 1.00; P = .05) for the association between glycolithocholate (GLCA) and obesity, indicating a marginal negative causal association. Consistent direction of the estimates obtained from the weighted median and MR-Egger methods was observed in the analysis of the association between GLCA and obesity. Furthermore, the IVW analysis demonstrated a suggestive association between GLCA and trunk fat percentage, with a beta value of -0.014 (95% confidence interval: -0.027, -0.0004; P = .04). Our findings suggest a potential negative causal relationship between GLCA and both obesity and trunk fat percentage, although no association survived corrections for multiple comparisons. These results indicate a trend towards a possible association between BAs and obesity, emphasizing the need for future studies.

Synthesis of bile acid-thiadiazole conjugates as antibacterial and antioxidant agents

The synthesis, characterization, and antibacterial and antioxidant activity of thiadiazole-deoxycholic/lithocholic acid conjugates are described in this communication. The structures of the synthesised bile acid-thiadiazole conjugates were studied using 1H NMR, 13C NMR and FTIR. Compounds 4c (IC50; 15.34 ± 0.07 μM) and 5c (IC50; 13.45 ± 0.25 μM) demonstrated greater antioxidant activity than the reference compound ascorbic acid (IC50; 20.72 ± 1.02 μM) in DPPH assay. The most effective conjugates against P. vulgarise were 4c (IC50; 24 ± 2.3 μM), 4 g (IC50; 29 ± 2.5 μM), and 5c (IC50; 93 ± 3.6 μM), whereas the most effective conjugates against E. coli were 4e (IC50; 55 ± 2.1 μM) and 4f (IC50; 52 ± 3.5 μM). Conjugates 4c and 5c were the most effective against B. megaterium of all the synthesised conjugates, with IC50 values of 15 ± 1.08 and 20 ± 1.1 μM, respectively. Thus, a large library of compounds derived from bile acid can be easily synthesised for extensive structure-activity relationship studies in order to identify the most appropriate antibacterial agents and antioxidant activity.

Oral Delivery of Gemcitabine-Loaded Glycocholic Acid-Modified Micelles for Cancer Therapy

The clinical utility of gemcitabine, an antimetabolite antineoplastic agent applied in various chemotherapy treatments, is limited due to the required intravenous injection. Although chemical structure modifications of gemcitabine result in enhanced oral bioavailability, these modifications compromise complex synthetic routes and cause unexpected side effects. In this study, gemcitabine-loaded glycocholic acid-modified micelles (Gem-PPG) were prepared for enhanced oral chemotherapy. The in vitro transport pathway experiments revealed that intact Gem-PPG were transported across the intestinal epithelial monolayer via an apical sodium-dependent bile acid transporter (ASBT)-mediated pathway. In mice, the pharmacokinetic analyses demonstrated that the oral bioavailability of Gem-PPG approached 81%, compared to less than 20% for unmodified micelles. In addition, the antitumor activity of oral Gem-PPG (30 mg/kg, BIW) was superior to that of free drug injection (60 mg/kg, BIW) in the xenograft model. Moreover, the assessments of hematology, blood chemistry, and histology all indicated the hypotoxicity profile of the drug-loaded micelles.

Synthesis and biological evaluation of cholic acid-conjugated oxaliplatin as a new prodrug for liver cancer

A cholic acid-conjugated oxaliplatin, LLC-202, is developed as a novel prodrug for liver cancer. The conjugate is obtained by using 3-NH_2-cyclobutane-1,1-dicarboxylate as a linker between the oxaliplatin analogue and cholic acid moiety and cholic acid is strongly bonded to the linker via an amide bond. Pharmacokinetic experiment shows that LLC-202 is mainly distributed and accumulated in the liver after intravenous administration to Sprague-Dawley rats, revealing the liver-targeting profile. Compared to oxaliplatin, LLC-202 is more easily taken up by human liver cancer cells than normal human liver cells. LLC-202 exhibits higher in vitro anticancer activity and higher efficacy comparable to oxaliplatin in treating primary hepatocellular carcinoma in C57BL/6 mice. It can significantly prolong the survival time of tumor-bearing mice by inducing apoptosis and inhibiting proliferation of cancer cells. In addition, LLC-202 shows less cytotoxicity toward normal human liver cells than oxaliplatin. Its acute toxicity in healthy Kunming (KM) mice after i.v. administration is comparable to oxaliplatin. Histopathological examination reveals that the main toxicity of LLC-202 in mice is the depression of bone marrow hematopoietic cells. The results suggest that LLC-202 has great potential for further development as a new prodrug specific for liver cancer.

Design, synthesis, characterization and anticancer activity evaluation of deoxycholic acid-chalcone conjugates

A series of deoxycholic acid-chalcone amides were synthesised and tested against the human lung cancer cell line, A549 and the cervical cancer cell line, SiHa. Among the synthesised deoxycholic acid-chalcone conjugates, some conjugates showed encouraging results as anticancer agents with good in vitro activity. More precisely, deoxycholic acid-chalcone conjugates 4b (IC50: 0.51 μM) and 4e (IC50: 0.84 μM) having 2‑nitrophenyl and 3,4,5‑trimethoxyphenyl groups exhibited a good activity against human cancer cell-line SiHa and while 4d (IC50: 0.25 μM) and 4b (IC50: 1.71 μM) showed better activity against A549 lung cancer cell line with respect to deoxycholic acid and chalcones. The anticancer activity of the bile acid conjugated chalcones was more than the activity of chalcone and deoxycholic acid alone. The results indicate that a bile acid conjugate strategy may be beneficial in improving the biological activity of chalcone derivatives. The enhanced activity of certain compounds may be due to their increased bioavailability.

Bile Acids Transporters of Enterohepatic Circulation for Targeted Drug Delivery

Bile acids (BAs) are important steroidal molecules with a rapidly growing span of applications across a variety of fields such as supramolecular chemistry, pharmacy, and biomedicine. This work provides a systematic review on their transport processes within the enterohepatic circulation and related processes. The focus is laid on the description of specific or less-specific BA transport proteins and their localization. Initially, the reader is provided with essential information about BAs′ properties, their systemic flow, metabolism, and functions. Later, the transport processes are described in detail and schematically illustrated, moving step by step from the liver via bile ducts to the gallbladder, small intestine, and colon; this description is accompanied by descriptions of major proteins known to be involved in BA transport. Spillage of BAs into systemic circulation and urine excretion are also discussed. Finally, the review also points out some of the less-studied areas of the enterohepatic circulation, which can be crucial for the development of BA-related drugs, prodrugs, and drug carrier systems.

Liver-targeted delivery of asiatic acid nanostructured lipid carrier for the treatment of liver fibrosis

Liver fibrosis is a major global health concern. Management of chronic liver disease is severely restricted in clinics due to ineffective treatment approaches. However, a lack of targeted therapy may aggravate this condition. Asiatic acid (AA), a pentacyclic triterpenoid acid, can effectively protect the liver from hepatic disorders. However, the pharmaceutical application of AA is limited by low oral bioavailability and poor targeting efficiency. This study synthesized a novel liver-targeting material from PEG-SA, chemically linked to ursodeoxycholic acid (UA), and utilized it to modify AA nanostructured lipid carriers (UP-AA-NLC) with enhanced targeting and improved efficacy. The formulation of UP-AA-NLC was optimized via the Box–Behnken Experimental Design (BBD) and characterized by size, zeta potential, TEM, DSC, and XRD. Furthermore, in vitro antifibrotic activity and proliferation of AA and NLCs were assessed in LX-2 cells. The addition of UP-AA-NLC significantly stimulated the TGF-beta1-induced expression of α-SMA, FN1, and Col I α1. In vivo near-infrared fluorescence imaging and distribution trials in rats demonstrated that UP-AA-NLC could significantly improve oral absorption and liver-targeting efficiency. Oral UP-AA-NLC greatly alleviated carbon tetrachloride-induced liver injury and fibrosis in rats in a dosage-dependent manner, as reflected by serum biochemical parameters (AST, ALT, and ALB), histopathological features (H&E and Masson staining), and antioxidant activity parameters (SOD and MDA). Also, treatment with UP-AA-NLC lowered liver hydroxyproline levels, demonstrating a reduction of collagen accumulation in the fibrotic liver. Collectively, optimized UP-AA-NLC has potential application prospects in liver-targeted therapy and holds great promise as a drug delivery system for treating liver diseases.

The Transporter-Mediated Cellular Uptake and Efflux of Pharmaceutical Drugs and Biotechnology Products: How and Why Phospholipid Bilayer Transport Is Negligible in Real Biomembranes

Over the years, my colleagues and I have come to realise that the likelihood of pharmaceutical drugs being able to diffuse through whatever unhindered phospholipid bilayer may exist in intact biological membranes in vivo is vanishingly low. This is because (i) most real biomembranes are mostly protein, not lipid, (ii) unlike purely lipid bilayers that can form transient aqueous channels, the high concentrations of proteins serve to stop such activity, (iii) natural evolution long ago selected against transport methods that just let any undesirable products enter a cell, (iv) transporters have now been identified for all kinds of molecules (even water) that were once thought not to require them, (v) many experiments show a massive variation in the uptake of drugs between different cells, tissues, and organisms, that cannot be explained if lipid bilayer transport is significant or if efflux were the only differentiator, and (vi) many experiments that manipulate the expression level of individual transporters as an independent variable demonstrate their role in drug and nutrient uptake (including in cytotoxicity or adverse drug reactions). This makes such transporters valuable both as a means of targeting drugs (not least anti-infectives) to selected cells or tissues and also as drug targets. The same considerations apply to the exploitation of substrate uptake and product efflux transporters in biotechnology. We are also beginning to recognise that transporters are more promiscuous, and antiporter activity is much more widespread, than had been realised, and that such processes are adaptive (i.e., were selected by natural evolution). The purpose of the present review is to summarise the above, and to rehearse and update readers on recent developments. These developments lead us to retain and indeed to strengthen our contention that for transmembrane pharmaceutical drug transport "phospholipid bilayer transport is negligible".

Research progress in the application of bile acid-drug conjugates: A "trojan horse" strategy

Bile acid transporters are highly expressed in intestinal cells and hepatocytes, and they determine the uptake of drugs in cells by modulating cellular entry and exit. In order to improve the oral bioavailability of drugs and investigate the potential application prospects of drugs used to target cancer, numerous studies have adopted these transporters to identify prodrug strategies. Through the connection of covalent bonds between drugs and bile acids, the resulting bile acid-drug conjugates continue to be recognized as similar to natural unmodified bile acid and is translocated by the transporter. The present mini-review provides a brief summary of recent progress of the application of bile acid-drug conjugates based primarily on ASBT, NTCP, and OATP, with the hope of contributing to subsequent research.

Apoptosis inducing properties of 3-biotinylate-6-benzimidazole B-nor-cholesterol analogues

In this work, a series of Biotin-substituted B-nor-cholesteryl benzimidazole compounds were synthesized. The antiproliferativeactivities of these compounds were evaluated in vitro using a series of human cancer cell lines, including HeLa (cervical cancer), SKOV3 (ovarian cancer), T-47D (thymus gland cancer), MCF-7 (human breast cancer) and HEK293T (normal renal epithelial) cells. These compounds displayed distinct antiproliferative activities against the currently tested cancer cells. The apoptotic properties induced by compound 6d were further investigated. Our results showed that compound 6d could induce the apoptosis of SKOV3 cells, blocking the cell growth in S-phase. Western blotting analyses revealed that compound 6d can induce cell apoptosis via the mitochondria-dependent pathway.

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.

An engineered disulfide bridge traps and validates an outward-facing conformation in a bile acid transporter

Apical sodium-dependent bile acid transporter (ASBT) mediates the uptake of bile acids from the ileum lumen into enterocytes and presents a potential target for the treatment of several metabolic diseases, including type 2 diabetes. It has been proposed that the underlying mechanism for transport by ASBT is an elevator-style alternating-access model, which was deduced mainly by comparing high-resolution structures of two bacterial ASBT homologs (ASBT_NM from Neisseria meningitides and ASBT_Yf from Yersinia frederiksenii) in different conformations. However, one important issue is that the only outward-facing structure (PDB entry 4n7x) was obtained with an Na⁺-binding site mutant of ASBT_Yf, which severely cripples its transport function, and therefore the physiological relevance of the conformation in PDB entry 4n7x requires further careful evaluation. Here, another crystal structure is reported of ASBT_Yf that was captured in a state closely resembling the conformation in PDB entry 4n7x using an engineered disulfide bridge. The introduced cysteine mutations avoided any proposed Na⁺- or substrate-binding residues, and the resulting mutant retained both structural and functional integrity and behaved similarly to wild-type ASBT_Yf. These data support the hypothesis that the PDB entry 4n7x-like structure represents a functional outward-facing conformation of ASBT_Yf in its transport cycle.

Recent advances in the bile acid based conjugates/derivatives towards their gelation applications

Bile acids have contributed immensely to hydrogel research due to their peculiar physicochemical properties and biocompatibility. The wide accessibility of bile acids and their straightforward derivatization methods make them attractive building blocks for the design of novel hydrogels systems to deliver biomolecules, drugs, and vaccines. This review conceptualizes recent developments in bile acid-based hydrogels and their applications. These bile-based hydrogels have the ability to absorb carbon dioxide efficiently and may potentially work as alternative materials for carbon dioxide capture and storage. The hydrogels hold great potential in medicine and biology applications as drug carriers and models for fundamental self-assembly in pathological conditions. Herein, we have summarized the efforts that have been made for the development of molecular hydrogels in terms of biocompatibility, therapeutic applications, and challenges associated with existing molecular hydrogels.

Bile Acid Conjugates with Anticancer Activity: Most Recent Research

The advantages of a treatment modality that combines two or more therapeutic agents in cancer therapy encourages the study of hybrid functional compounds for pharmacological applications. In light of this, we reviewed recent works on hybrid molecules based on bile acids. Due to their biological properties, as well as their different chemical/biochemical reactive moieties, bile acids can be considered very interesting starting molecules for conjugation with natural or synthetic bioactive molecules.

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.

Evaluation of the Anticancer Activity of a Bile Acid-Dihydroartemisinin Hybrid Ursodeoxycholic-Dihydroartemisinin in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy in adults and accounts for 85-90% of all primary liver cancer. Based on the estimation by the International Agency for Research on Cancer in 2018, liver cancer is the fourth leading cause of cancer death globally. Dihydroartemisinin (DHA), the main active metabolite of artemisinin derivatives, is a well-known drug for the treatment of malaria. Previous studies have demonstrated that DHA exhibits antitumor effects toward a variety of human cancers and has a potential for repurposing as an anticancer drug. However, its short half-life is a concern and may limit the application in cancer therapy. We have reported that UDC-DHA, a hybrid of bile acid ursodeoxycholic acid (UDCA) and DHA, is ∼12 times more potent than DHA against a HCC cell line HepG2. In this study, we found that UDC-DHA was also effective against another HCC cell line Huh-7 with an IC₅₀ of 2.16 μM, which was 18.5-fold better than DHA with an IC₅₀ of 39.96 μM. UDC-DHA was much more potent than the combination of DHA and UDCA at 1:1 molar ratio, suggesting that the covalent linkage rather than a synergism between UDCA and DHA is critical for enhancing DHA potency in HepG2 cells. Importantly, UDC-DHA was much less toxic to normal cells than DHA. UDC-DHA induced G0/G1 arrest and apoptosis. Both DHA and UDC-DHA significantly elevated cellular reactive oxygen species generation but with different magnitude and timing in HepG2 cells; whereas only DHA but not UDC-DHA induced reactive oxygen species in Huh-7 cells. Depolarization of mitochondrial membrane potential was detected in both HepG2 and Huh-7 cells and may contribute to the anticancer effect of DHA and UDC-DHA. Furthermore, UDC-DHA was much more stable than DHA based on activity assays and high performance liquid chromatography-MS/MS analysis. In conclusion, UDC-DHA and DHA may exert anticancer actions via similar mechanisms but a much lower concentration of UDC-DHA was required, which could be attributed to a better stability of UDC-DHA. Thus, UDC-DHA could be a better drug candidate than DHA against HCC and further investigation is warranted.

Bile acid transporter-mediated oral drug delivery

Bile acids are synthesized in the liver, stored in the gallbladder, and secreted into the duodenum at meals. Apical sodium-dependent bile acid transporter (ASBT), an ileal Na⁺-dependent transporter, plays the leading role of bile acid absorption into enterocytes, where bile acids are delivered to basolateral side by ileal bile acid binding protein (IBABP) and then released by organic solute transporter OSTα/β. The absorbed bile acids are delivered to the liver via portal vein. In this process called "enterohepatic recycling", only 5% of the bile acid pool (~3 g in human) is excreted in feces, indicating the large recycling capacity and high transport efficacy of ASBT-mediated absorption. Therefore, bile acid transporter-mediated oral drug delivery has been regarded as a feasible and potential strategy to improve the oral bioavailability. This review introduces the key factors in enterohepatic recycling, especially the mechanism of bile acid uptake by ASBT, and the development of bile acid-based oral drug delivery for ASBT-targeting, including bile acid-based prodrugs, bile acid/drug electrostatic complexation and bile acid-containing nanocarriers. Furthermore, the specific transport pathways of bile acid in enterocytes are described and the recent finding of lymphatic delivery of bile acid-containing nanocarriers is discussed.

Updates in bile acid-bioactive molecule conjugates and their applications

Bile acid conjugates are emerging as important chemical resources due to their low cost and wide availability of bile acids, making them privileged molecules in drug carrier systems and building blocks for derivatization and chiral template introduction into bioactive molecules. In recent years, bile acids as scaffolds in supramolecular, medicinal, and material chemistry attracted prime focus of researchers as an area of research to be followed with passion. Due to peculiar physicochemical and biological properties, bile acid exhibited various applications in biomedical and pharmaceutical fields. In this review, the bile acid conjugations with different bioactive compounds have been discussed to understand their influence on the bioavailability of bioactive compounds.

Modifications on the heterocyclic base of ganciclovir, penciclovir, acyclovir - syntheses and antiviral properties

АBSTRACTEsters of the antiherpetic drugs ganciclovir, penciclovir with the bile acids (cholic, chenodeoxycholic and deoxycholic) and amino acid esters of acyclovir were generated and evaluated for their in vitro antiviral activity against herpes simplex viruses type 1 and type 2 (HSV-1, HSV-2). The antiviral assays demonstrated that modified analogs of ACV and PCV are less active compared to the initial substances against HSV-1and HSV-2. CC50 for ganciclovir-deoxycholate corresponded to the CC50 of the other analogs and its activity is lower than ganciclovir. Obtained results show that tested modification do not improve bioavailability of nucleoside analogs in cells.

Design, Synthesis, and Anti-bacterial Activity of Novel Deoxycholic Acid- Amino Alcohol Conjugates

Background:

Numerous synthetic bile acid derivatives have been recognized for their various biological activities. Among these, bile acid amides have emerged as an attractive antibacterial agent. We herein illustrate the synthesis and antibacterial evaluation of deoxycholic acidamino alcohols conjugates.

Objective:

Design and Synthesis of novel deoxycholic acid-amino alcohol conjugates to investigate their antibacterial activity against E. coli and S. aureus.

Methods:

Novel deoxycholic acid-amino alcohol conjugates were synthesized, from conjugation of deoxycholic acid-NHS ester with amino alcohols. Various amino alcohols moieties were appended to the C24 position of deoxycholic acid to yield deoxycholic acid-amino alcohol conjugates. All the synthesized compounds were characterized by 1H NMR, 13C NMR, IR and massspectroscopy. The entire synthesized deoxycholic acid-amino alcohol conjugates were evaluated for their antibacterial activity against E. coli and S. aureus using the broth dilution method.

Results:

The outcome illustrated that some of the novel deoxycholic acid-amino alcohol conjugates exhibited enhanced anti-bacterial activities. Amongst them, deoxycholic acid-amino alcohol conjugate containing (-R)-2-aminocyclohexanol (1) demonstrated promising efficacy against both strains S. aureus ATCC 25923 (MIC 15 μg/mL) and E. coli ATCC 25922 (MIC 45 μg/mL) and was identified as a lead molecule.

Conclusion:

Numbers of novel deoxycholic acid-amino alcohol conjugates were synthesized and their antimicrobial activities provided useful information that the potency was strongly depending on the structures of deoxycholic acid-amino alcohol conjugates.

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.

Recent methods for diversification of bile acids and related steroids towards supramolecular

Bile acids (BAs) are a class of steroidal surfactants that have been studied as building blocks for constructing useful chemical frameworks. These starting materials have rigid structures with defined hydrophobic and hydrophilic faces, which promotes self-assembly in well-defined chemical architectures. The BA scaffolds can undergo a variety of transformations to introduce a range functionalities with practical applications. These functionalized derivatives have seen application in pharmacology, supramolecular chemistry, and nanotechnology in roles such as surfactants, gelators, drug conjugates, or chemical detectors. This review seeks to highlight recent synthetic methods utilizing BAs to construct useful chemical structures and their application in supramolecular chemistry.

Induction of a non-apoptotic mode of cell death associated with autophagic characteristics with steroidal maleic anhydrides and 7β-hydroxycholesterol on glioma cells

Steroidal maleic anhydrides were prepared in one step: lithocholic, chenodeoxicholic, deoxicholic, ursocholic, and hyodeoxicholic acid derivatives. Their capability to induce cell death was studied on C6 rat glioma cells, and 7β-hydroxycholesterol was used as positive cytotoxic control. The highest cytotoxicity was observed with lithocholic and chenodeoxicholic acid derivatives (23-(4-methylfuran-2,5-dione)-3α-hydroxy-24-nor-5β-cholane (compound 1a), and 23-(4-methylfuran-2,5-dione)-3α,7α-dihydroxy-24-nor-5β-cholane (compound 1b), respectively), which induce a non-apoptotic mode of cell death associated with mitochondrial membrane potential loss and reactive oxygen species overproduction. No cells with condensed and/or fragmented nuclei, no PARP degradation and no cleaved-caspase-3, which are apoptotic criteria, were observed. Similar effects were found with 7β-hydroxycholesterol. The cell clonogenic survival assay showed that compound 1b was more cytotoxic than compound 1a and 7β-hydroxycholesterol. Compound 1b and 7β-hydroxycholesterol also induce cell cycle modifications. In addition, compounds 1a and 1b, and 7β-hydroxycholesterol favour the formation of large acidic vacuoles revealed by staining with acridine orange and monodansylcadaverine evocating autophagic vacuoles; they also induce an increased ratio of [LC3-II / LC3-I], and modify the expression of mTOR, Beclin-1, Atg12, and Atg5-Atg12 which is are autophagic criteria. The ratio [LC3-II / LC3-I] is also strongly modified by bafilomycin acting on the autophagic flux. Rapamycin, an autophagic inducer, and 3-methyladenine, an autophagic inhibitor, reduce and increase 7β-hydroxycholesterol-induced cell death, respectively, supporting that 7β-hydroxycholesterol induces survival autophagy. Alpha-tocopherol also strongly attenuates 7β-hydroxycholesterol-induced cell death. However, rapamycin, 3-methyladenine, and α-tocopherol have no effect on compounds 1a and 1b-induced cell death. It is concluded that these compounds trigger a non apoptotic mode of cell death, involving the mitochondria and associated with several characteristics of autophagy.

Targeted delivery of atorvastatin via asialoglycoprotein receptor (ASGPR)

Targeted drug delivery platforms can increase the concentration of drugs in specific cell populations, reduce adverse effects, and hence improve the therapeutic effect of drugs. Herein, we designed two conjugates by installing the targeting ligand GalNAc (N-acetylgalactosamine) onto atorvastatin (AT). Compared to the parent drug, these two conjugates, termed G2-AT and G2-K-AT, showed increased hepatic cellular uptake. Moreover, both conjugates were able to release atorvastatin, and consequently showed dramatic inhibition of β-hydroxy-β-methylglutaryl-CoA (HMG-CoA) reductase and increased LDL receptors on cell surface.

Bile acids and the metabolic syndrome

Bile acids have important roles in the regulation of lipid, glucose and energy metabolism. Metabolic diseases linked to obesity, including type 2 diabetes mellitus and non-alcoholic fatty liver disease, are associated with dysregulation of bile acid homeostasis. Here, the basic chemistry and regulation of bile acids as well as their metabolic effects will be reviewed. Changes in circulating bile acids associated with obesity and related diseases will be reviewed. Finally, pharmaceutical manipulation of bile acid homeostasis as therapy for metabolic diseases will be outlined.

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

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

A novel bioluminescence-based method to investigate uptake of bile acids in living cells

Bile acid transporters, including the ileal apical sodium-dependent bile acid transporter (ASBT) and the hepatic sodium-taurocholate cotransporting polypeptide (NTCP), are crucial for the enterohepatic circulation of bile acids. Our objective was to develop a method for measuring bile acid transporter activity in real time to precisely evaluate rapid changes in their function. We designed a reporter system relying on a novel probe: cholic acid attached to luciferin via a disulfide-containing, self-immolating linker (CA-SS-Luc). Incubation of human embryonic kidney-293 cells coexpressing luciferase and ASBT with different concentrations of CA-SS-Luc (0.01-1 μM) resulted in bioluminescence with an intensity that was concentration- and time-dependent. The bioluminescence measured during incubation with 1 μM CA-SS-Luc was dependent on the levels of ASBT or NTCP expressed in the cells. Coincubation of CA-SS-Luc with natural bile acids enhanced the bioluminescence in a concentration-dependent manner with kinetic parameters for ASBT similar to those previously reported using conventional methods. These findings suggest that this method faithfully assesses ASBT function. Further, incubation with tyrosine phosphatase inhibitor III (PTPIII) led to significantly increased bioluminescence in cells expressing ASBT, consistent with previous studies showing an increase in ASBT function by PTPIII. We then investigated CA-SS-Luc in isolated mouse intestinal epithelial cells. Ileal enterocytes displayed significantly higher luminescence compared with jejunal enterocytes, indicating a transport process mediated by ileal ASBT. In conclusion, we have developed a novel method to monitor the activity of bile acid transporters in real time that has potential applications both for in vitro and in vivo studies. NEW & NOTEWORTHY This article reports the development of a real-time method for measuring the uptake of bile acids using a bioluminescent bile acid-based probe. This method has been validated for measuring uptake via the apical sodium-dependent bile acid transporter and the sodium-taurocholate cotransporting polypeptide in cell culture and ex vivo intestinal models.

Metallomics for Alzheimer's disease treatment: Use of new generation of chelators combining metal-cation binding and transport properties

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting tens of million people. Currently marketed drugs have limited therapeutic efficacy and only slowing down the neurodegenerative process. Interestingly, it has been suggested that biometal cations in the amyloid beta (Aβ) aggregate deposits contribute to neurotoxicity and degenerative changes in AD. Thus, chelation therapy could represent novel mode of therapeutic intervention. Here we describe the features of chelators with therapeutically relevant mechanism of action. We have found that the tested compounds effectively reduce the toxicity of exogenous Aβ and suppress its endogenous production as well as decrease oxidative stress. Cholyl hydrazones were found to be the most active compounds. In summary, our data show that cation complexation, together with improving transport efficacy may represent basis for eventual treatment strategy in AD.

Oral siRNA Delivery to Treat Colorectal Liver Metastases

Convenient multiple dosing makes oral administration an ideal route for delivery of therapeutic siRNA. However, hostile GI environments and nonspecific biological trafficking prevent achieving appropriate bioavailability of siRNA. Here, an orally administered AuNP-siRNA-glycol chitosan-taurocholic acid nanoparticle (AR-GT NPs) was developed to selectively deliver Akt2 siRNA and treat colorectal liver metastases (CLM). AR-GT NPs are dual padlocked nonviral vectors in which the initially formed AuNP-siRNA (AR) conjugates are further encompassed by bifunctional glycol chitosan-taurocholic acid (GT) conjugates. Covering the surface of AR with GT protected the Akt2 siRNA from GI degradation, facilitated active transport through enterocytes, and enhanced selective accumulation in CLM. Our studies in CLM animal models resulted in the reduction in Akt2 production, followed by initiation of apoptosis in cancer cells after oral administration of Akt2 siRNA-loaded AR-GT. This therapeutic siRNA delivery system may be a promising approach in treating liver-associated diseases.

Protecting group-free radical decarboxylation of bile acids: Synthesis of novel steroidal substituted maleic anhydrides and maleimides and evaluation of their cytotoxicity on C6 rat glioma cells

We report the first Barton radical decarboxylation of unprotected bile acids via in situ irradiation of their thiohydroxamic esters in the presence of citraconic anhydride and citracoimide, leading to the synthesis a series of steroidal maleic anhydrides and maleimides as novel hybrid bile acids. The cytotoxic activities were evaluated on C6 rat glioma cells.

Effects of Karela (Bitter Melon; Momordica charantia) on genes of lipids and carbohydrates metabolism in experimental hypercholesterolemia: biochemical, molecular and histopathological study

Background

Hypercholesterolemia is a serious diseases associated with type-2 diabetes, atherosclerosis, cardiovascular disorders and liver diseases. Humans seek for safe herbal medication such as karela (Momordica charantia/bitter melon) to treat such disorders to avoid side effect of pharmacotherapies widely used.

Methods

Forty male Wistar rats were divided into four equal groups; control group with free access to food and water, cholesterol administered group (40 mg/kg BW orally); karela administered group (5 g /kg BW orally) and mixture of cholesterol and karela. The treatments continued for 10 weeks. Karela was given for hypercholesterolemic rats after 6 weeks of cholesterol administration. Serum, liver and epididymal adipose tissues were taken for biochemical, histopathological and genetic assessments.

Results

Hypercholesterolemia induced a decrease in serum superoxide dismutase (SOD), catalase, reduced glutathione (GSH) and an increase in malondialdehyde (MDA) levels that were ameliorated by karela administration. Hypercholesterolemia up regulated antioxidants mRNA expression and altered the expression of carbohydrate metabolism genes. In parallel, hypercholesterolemic groups showed significant changes in the expression of PPAR-alpha and gamma, lipolysis, lipogenesis and cholesterol metabolism such as carnitine palmitoyltransferase-1 (CPT-1). Acyl CoA oxidase (ACO), fatty acids synthase (FAS), sterol responsible element binding protein-1c (SREBP1c), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoAR) and cholesterol 7α-hydroxylase (CYP7A1) at hepatic and adipose tissue levels. Interestingly, Karela ameliorated all altered genes confirming its hypocholesterolemic effect. Histopathological and immunohistochemical findings revealed that hypercholesterolemia induced hepatic tissue changes compared with control. These changes include cholesterol clefts, necrosis, karyolysis and sever congestion of portal blood vessel. Caspase-3 immunoreactivity showed positive expression in hepatic cells of hypercholesterolemic rats compared to control. All were counteracted and normalized after Karela administration to hypercholesterolemic group.

Conclusion

Current findings confirmed that karela is a potential supplement useful in treatment of hypercholesterolemia and its associated disorders and is good for human health.

Novel Liver-targeted conjugates of Glycogen Phosphorylase Inhibitor PSN-357 for the Treatment of Diabetes: Design, Synthesis, Pharmacokinetic and Pharmacological Evaluations

PSN-357, an effective glycogen phosphorylase (GP) inhibitor for the treatment for type 2 diabetics, is hampered in its clinical use by the poor selectivity between the GP isoforms in liver and in skeletal muscle. In this study, by the introduction of cholic acid, 9 novel potent and liver-targeted conjugates of PSN-357 were obtained. Among these conjugates, conjugate 6 exhibited slight GP inhibitory activity (IC₅₀ = 31.17 μM), good cellular efficacy (IC₅₀ = 13.39 μM) and suitable stability under various conditions. The distribution and pharmacokinetic studies revealed that conjugate 6 could redistribute from plasma to liver resulting in a considerable higher exposure of PSN-357 metabolizing from 6 in liver (AUC_liver/AUC_plasma ratio was 18.74) vs that of PSN-357 (AUC_liver/AUC_plasma ratio was 10.06). In the in vivo animal study of hypoglycemia under the same dose of 50 mg/kg, conjugate 6 exhibited a small but significant hypoglycemic effects in longer-acting manners, that the hypoglycemic effects of 6 is somewhat weaker than PSN-357 from administration up to 6 h, and then became higher than PSN-357 for the rest time of the test. Those results indicate that the liver-targeted glycogen phosphorylase inhibitor may hold utility in the treatment of type 2 diabetes.

Pharmacokinetic studies of novel berberine derivatives with ultra-performance liquid chromatography-tandem mass spectrometry

An ultra-performance liquid chromatography with tandem mass spectrometric detection method was developed for the detection of berberine and its derivatives (A4, B4) in rat plasma and other organs. This validated method was successfully applied to our pharmacokinetic study of BBR derivatives in rats. At the same dose of administration, the Cmax of B4 was about eight times higher than BBR, and its half-life was approximately two times longer than BBR, according to the bigger areas under plasma concentration curves. Inversely, the pharmacokinetic parameter levels of A4 were all inferior to BBR, suggesting a tight structure-activity relationship of these compounds. Small dose of parenteral administration was used for the study of absolute oral bioavailability of A4, B4, and BBR, and the results calculated were 0.12%, 3.4% and 0.7%, respectively. The accumulations of B4 among all organs were intestine>liver>heart>kidney>lung>spleen>plasma, proving a deeply targeting property of B4, which met our experimental assumption. Together, the experimental results proved that compared with BBR and A4, the derivative B4 had higher absolute oral bioavailability and the ability of deeply targeting so that can be likely used in some organ-targeted diseases.

The effect of a tertiary bile acid, taurocholic acid, on the morphology and physical characteristics of microencapsulated probucol: potential applications in diabetes: a characterization study

In recent studies, we designed multi-compartmental microcapsules as a platform for the targeted oral delivery of lipophilic drugs in an animal model of type 2 diabetes (T2D). Probucol (PB) is a highly lipophilic, antihyperlipidemic drug with potential antidiabetic effects. PB has low bioavailability and high inter-individual variations in absorption, which limits its clinical applications. In a new study, the bile acid, taurocholic acid (TCA), exerted permeation enhancing effects in vivo. Accordingly, this study aimed to design and characterize TCA-based PB microcapsules and examine the effects of TCA on the microcapsules' morphology, stability, and release profiles. Microcapsules were prepared using the polymer sodium alginate (SA). Two types of microcapsules were produced, one without TCA (PB-SA, control) and one with TCA (PB-TCA-SA, test). Microcapsules were studied in terms of morphology, surface structure and composition, size, drug contents, cross-sectional imaging (using microtomography (Micro-CT) analysis), Zeta potential, thermal and chemical profiles, rheological parameters, swelling, mechanical strength, and release studies at various temperature and pH values. The production yield and the encapsulation efficiency were also studied together with in vitro efficacy testing of cell viability at various glucose concentrations and insulin and TNF-α production using clonal-mouse pancreatic β-cells. PB-TCA-SA microcapsules showed uniform structure and even distribution of TCA within the microcapsules. Drug contents, Zeta potential, size, rheological parameters, production yield, and the microencapsulation efficiency remained similar after TCA addition. In vitro testing showed PB-TCA-SA microcapsules improved β-cell survival under hyperglycemic states and reduced the pro-inflammatory cytokine TNF-α while increasing insulin secretions compared with PB-SA microcapsules. PB-TCA-SA microcapsules also showed good stability, better mechanical (p < 0.01) and swelling (p < 0.01) characteristics, and optimized controlled release at pH 7.8 (p < 0.01) compared with control, suggesting desirable targeted release properties and potential applications in the oral delivery of PB in T2D.

Synthesis of cholic-acid-carrying polymer and in-vitro evaluation of hepatoma-targeting nanoparticles decorated with the polymer

The specific interaction between bile acids and the bile acids transporters provides a promising way for hepatoma-targeted drug delivery. We synthesized an amphipathic polymer containing cholic acid (CA), the main bile acids in body, and prepared CA-functionalized nanoparticles to target hepatoma cells. Poly-[3-(4-vinylbenzonate)-7, 12-dihydroxy-5-cholan-24-oic acid] (PVBCA) was synthesized by introducing methyl cholate onto polyvinyl benzoate polymer backbone, and was characterized by (1)H-NMR, FT-IR, and GFC. PVBCA can be incorporated onto PLGA nanoparticles surface via the emulsion-solvent evaporation procedure, resulting in the nanoparticles carrying CA moieties on their surface. The binding of CA moieties to the bile acids' transporters on the cell membrane enhances the cellular uptake of the nanoparticles significantly. The SMMC-7721 cell uptake of PVBCA-decorated nanoparticles increases with amount of incorporated PVBCA and is 2- to 2.8-fold higher than that of the normal PLGA nanoparticles. By exclusion of specific endocytosis pathways using chemical inhibitors, we found that the uptake mechanism of PVBCA-decorated nanoparticles was mainly attributed to clathrin-and-caveolae-independent endocytosis, which was distinct from that of PLGA nanoparticles. The present study provides a simple and versatile method for hepatoma-targeted delivery of nanoparticles.

Biocompatible hydrogelators based on bile acid ethyl amides

Four novel bile acid ethyl amides were synthetized using a well-known method. All the four compounds were characterized by IR, SEM, and X-ray crystal analyses. In addition, the cytotoxicity of the compounds was tested. Two of the prepared compounds formed organogels. Lithocholic acid derivative 1 formed hydrogels as 1% and 2% (w/v) in four different aqueous solutions. This is very intriguing regarding possible uses in biomedicine.

Therapeutic Effect of Chenodeoxycholic Acid in an Experimental Rabbit Model of Osteoarthritis

Osteoarthritis (OA) is a slowly progressive joint disease typically seen in middle-age to elderly people. At present, there is no ideal agent to treat OA. Chenodeoxycholic acid (CDCA) was a principal active constituent from animal bile. However, the therapeutic effect of CDCA on OA severity was largely unknown. The purpose of this study was to evaluate the therapeutic effect of intra-articular injection of CDCA in a rabbit OA model. OA was induced in experimental rabbits by anterior cruciate ligament transection (ACLT) and then rabbits were intra-articularly injected with CDCA (10 mg/kg or 50 mg/kg) once per week for 5 weeks. The results showed that CDCA significantly decreased cartilage degradation on the surface of femoral condyles, reducing the pathological changes of articular cartilage and synovial membrane by macroscopic and histological analysis. CDCA also significantly decreased bone destruction and erosion of joint evaluated by micro-CT. Furthermore, CDCA could markedly reduce the release of matrix metalloproteinase-1 (MMP-1), matrix metalloproteinase-3 (MMP-3), interleukin-1β (IL-1β), and prostaglandin E2 (PGE2) in synovial fluid. These observations highlight CDCA might be a potential therapeutic agent for OA.

Decreasing cartilage damage in a rat model of osteoarthritis by intra-articular injection of deoxycholic acid

BACKGROUND

The aim of this experimental study was to evaluate the effect of intra-articular injection of Deoxycholic acid (DCA) on articular cartilage and subchondral bone following induction of knee Osteoarthritis (OA) in a rat model.

METHODS

Twenty-four Sprague Dawley rats were randomized divided into 4 groups (n = 6). Eighteen of the 24 rats underwent surgical destabilization of the medial meniscus on the right knee joints to induce OA, were divided into 3 groups: DCA 30 mg/kg group, DCA 120 mg/kg group and OA group. The rats in DCA-treated groups were given intra-articular injections of DCA (30 mg/kg or 120 mg/kg) in the operated knees once per 3 days for 42 days. The rats in OA group given intra-articular injections of vehicle alone in the operated knees under the same conditions. The remaining 6 rats (sham-operation group) received sham operations on the right knee joints. 45 days postoperatively, all of the animals were euthanized for macroscopic, histological and radiographic analysis to evaluate the effect of DCA on OA and to determine its potential mechanisms.

RESULTS

The results showed that DCA attenuated the severity of OA by reducing macroscopic observation sores for femoral condyles and histological sores for articular cartilage. DCA also significantly decreased bone destruction and erosion of joint evaluated by radiographic examination. Furthermore, DCA could markedly reduce the release of MMP-1, MMP-3 and IL-1β in serum.

CONCLUSIONS

Intra-articular injection of DCA is beneficial for knee OA. It might repair and protect OA cartilage by delaying cartilage degeneration and impairing the function of inflammatory mediators. These findings highlight DCA might be a useful therapeutic agent for OA.