Sodium-dependent Bile Acid Transporter Research Articles

Redundant Functions of ERK1 and ERK2 Maintain Mouse Liver Homeostasis Through Down-Regulation of Bile Acid Synthesis.

Activation of extracellular signal–regulated kinase (ERK) 1/2 promotes hepatocyte proliferation in response to growth stimuli, but whether constitutive hepatocyte ERK1/2 signaling functions in liver physiology is unknown. To examine the role of ERK1/2 in hepatic homeostasis, the effects of a knockout of Erk1 and/or Erk2 in mouse liver were examined. The livers of mice with a global Erk1 knockout or a tamoxifen‐inducible, hepatocyte‐specific Erk2 knockout were normal. In contrast, Erk1/2 double‐knockout mice developed hepatomegaly and hepatitis by serum transaminases, histology, terminal deoxynucleotide transferase‐mediated deoxyuridine triphosphate nick end‐labeling, and assays of hepatic inflammation. Liver injury was associated with biochemical evidence of cholestasis with increased serum and hepatic bile acids and led to hepatic fibrosis and mortality. RNA sequencing and polymerase chain reaction analysis of double‐knockout mouse livers revealed that the rate‐limiting bile acid synthesis gene Cyp7a1 (cholesterol 7α‐hydroxylase) was up‐regulated in concert with decreased expression of the transcriptional repressor short heterodimer partner. Elevated bile acids were the mechanism of liver injury, as bile acid reduction by SC‐435, an inhibitor of the ileal apical sodium–dependent bile acid transporter, prevented liver injury. Conclusion: Constitutive ERK1 and ERK2 signaling has a redundant but critical physiological function in the down‐regulation of hepatic bile acid synthesis to maintain normal liver homeostasis.

Modulation of Bile Acid Metabolism to Improve Plasma Lipid and Lipoprotein Profiles.

New drugs targeting bile acid metabolism are currently being evaluated in clinical studies for their potential to treat cholestatic liver diseases, non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Changes in bile acid metabolism, however, translate into an alteration of plasma cholesterol and triglyceride concentrations, which may also affect cardiovascular outcomes in such patients. This review attempts to gain insight into this matter and improve our understanding of the interactions between bile acid and lipid metabolism. Bile acid sequestrants (BAS), which bind bile acids in the intestine and promote their faecal excretion, have long been used in the clinic to reduce LDL cholesterol and, thereby, atherosclerotic cardiovascular disease (ASCVD) risk. However, BAS modestly but consistently increase plasma triglycerides, which is considered a causal risk factor for ASCVD. Like BAS, inhibitors of the apical sodium-dependent bile acid transporter (ASBTi’s) reduce intestinal bile acid absorption. ASBTi’s show effects that are quite similar to those obtained with BAS, which is anticipated when considering that accelerated faecal loss of bile acids is compensated by an increased hepatic synthesis of bile acids from cholesterol. Oppositely, treatment with farnesoid X receptor agonists, resulting in inhibition of bile acid synthesis, appears to be associated with increased LDL cholesterol. In conclusion, the increasing efforts to employ drugs that intervene in bile acid metabolism and signalling pathways for the treatment of metabolic diseases such as NAFLD warrants reinforcing interactions between the bile acid and lipid and lipoprotein research fields. This review may be considered as the first step in this process.

Functional characterization of Clonorchis sinensis sodium-bile acid co-transporter (CsSBAT) as a steroid sulfate transporter.

Clonorchis sinensis (Cs) is a common trematode in Asian countries. Infection by Cs can result in many clinical symptoms. Here, a cDNA encoding a Cs apical sodium-dependent bile acid transporter (CsSBAT) was isolated from a Cs cDNA library, and functional characterization was performed using Xenopus laevis oocyte expression system. When expressed in Xenopus laevis oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate and dehydroepiandrosterone sulfate. No trans-uptake of carnitine, estradiol 17 β-D glucuronide, prostaglandin E2, p-aminohippuric acid, α-ketoglutaric acid, and tetraethylammonium was observed. CsSBAT-mediated estrone sulfate uptake was in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04μM for [3H]estrone sulfate. CsSBAT-mediated estrone sulfate uptake was strongly inhibited by sulfate conjugates but not glucuronide conjugates. These findings contribute to our understanding of CsSBAT transport properties and the cascade of estrogen metabolite movement in Cs.

Apical sodium-dependent bile acid transporter inhibition in children with Alagille syndrome

In The Lancet, Emmanuel Gonzales and colleagues 1 Gonzales E Hardikar W Stormon M et al. Efficacy and safety of maralixibat treatment in patients with Alagille syndrome and cholestatic pruritus (ICONIC): a randomised phase 2 study. Lancet. 2021; 398: 1581-1592 Google Scholar present the findings of the phase 2 placebo-controlled, randomised withdrawal period, open-label, extension ICONIC study of the apical sodium-dependent bile acid transporter (ASBT) inhibitor, maralixibat, in paediatric patients with Alagille syndrome. Alagille syndrome is a cholestatic liver disease that leads to pruritus, xanthomas, and impaired quality of life. Surgical interventions to interrupt the enterohepatic bile acid circulation or liver transplantation are often pursued 2 Wang KS Tiao G Bass LM et al. Analysis of surgical interruption of the enterohepatic circulation as a treatment for pediatric cholestasis. Hepatology. 2017; 65: 1645-1654 Google Scholar , 3 Kamath BM Ye W Goodrich NP et al. Outcomes of childhood cholestasis in Alagille syndrome: results of a multicenter observational study. Hepatol Commun. 2020; 4: 387-398 Google Scholar because there are no approved medical therapies. ASBT has a key role in the enterohepatic circulation of bile acids because it absorbs approximately 95% of bile acids from the terminal ileum. Because intrahepatic bile acids are thought to be the main driver behind hepatocellular injury in cholestatic diseases, pharmacological inhibition of ASBT has the potential to not only improve pruritus, but also disease trajectory. Studies in mouse models of cholestasis have shown that ASBT inhibition can decrease intrahepatic bile acid concentrations and improve fibrosis and disease progression. 4 Miethke AG Zhang W Simmons J et al. Pharmacological inhibition of apical sodium-dependent bile acid transporter changes bile composition and blocks progression of sclerosing cholangitis in multidrug resistance 2 knockout mice. Hepatology. 2016; 63: 512-523 Google Scholar , 5 Baghdasaryan A Fuchs CD Osterreicher CH et al. Inhibition of intestinal bile acid absorption improves cholestatic liver and bile duct injury in a mouse model of sclerosing cholangitis. J Hepatol. 2016; 64: 674-681 Google Scholar Efficacy and safety of maralixibat treatment in patients with Alagille syndrome and cholestatic pruritus (ICONIC): a randomised phase 2 studyIn children with Alagille syndrome, maralixibat is, to our knowledge, the first agent to show durable and clinically meaningful improvements in cholestasis. Maralixibat might represent a new treatment paradigm for chronic cholestasis in Alagille syndrome. Full-Text PDF

An Update on Management of Nonalcoholic Fatty Liver Disease & Nonalcoholic Steatohepapititis is the Time Ripe for Achieving Resolution of NAFLD & NASH Soon

We earlier reviewed how obesity has assumed an endemic/pandemicproportions that has resulted in escalating incidence and prevalence ofassociated escalating worldwide incidence of Metabolic Syndrome (MetS)with non alcoholic fatty liver disease (NAFLD), that is correlated withenhanced morbidity. Later we tried to detail how probiotics, L-Carnitine(LC), Nicotinamide Ribose (NR) Combination, along with Apical SodiumDependent Bile Acids Transporter (ASBT) or Volixibat and Silybin,Vitamin D, Allyl Isothiocyanate (AITC), might aid in treating andunderstand the etiopathogenesis of NAFLD. The prevalence of NAFLDall over the world is approximately 25%, with that of non alcoholicsteatohepapititis (NASH), varying from 1.5%=6.45%. Particularly NASH,specifically the ones associated with fibrosis possess a greater chance ofgeneration of side effects that include progression to cirrhosis as well asliver-associated mortality. Despite an improvement was observed withvitamin E, Pioglitazone. liraglutide in histological appearance in liverrandomized controlled clinical trials (RCT), at present no drugs existsthat have received FDI approval for NASH. The aim of this review wasto update the newer drugs getting evaluated, undergoing phase 2-3 trials.Currently there are Obeticholic acid, elafibranor, cenicriviroc, resmetriom,in addition to aramchol, that are the five agents that are getting analysedin big, histology dependent phase 3 trials. Hopefully within another 2-4years, newer, efficacious drugs will be available for the therapy of NASH.Besides that a lot of phase 2 trials are continuing for different drugs.Further depending on outcomes of phase 2-3 trials, combination treatmentsare getting evaluated. For future therapeutic approaches would be madeup of variations in NASH phenotypes, besides personalized approachesbased on various NASH phenotypes in addition to response of every singlepatient. Further recently there were reports of utilization of curcumin withnonselective beta blocker for regression from cirrhosis (reviewed by us).Hopefully once there are approved therapies for NAFLD/NASH, we canwork in that direction.

Bile acid transporter-mediated oral absorption of insulin via hydrophobic ion-pairing approach

Despite many ongoing and innovative approaches, there are still formidable challenges in the clinical translation of oral peptide drugs into marketable products due to their low absorption and poor bioavailability. Herein, a novel nanocarrier platform was developed that employs a hydrophobic ion-pairing (HIP) of model peptide (insulin) and the anionic bile salt (sodium glycodeoxycholate, SGDC), and markedly improves intestinal absorption via the bile acid pathway. The developed HIP-nanocomplexes (C1 and C2) were optimized, characterized, and in vitro and in vivo evaluation were performed to assess oral efficacy of these system. The optimal molar ratios of C1 and C2-nanocomplexes were 30:1 and 6:1 (SGDC:insulin), respectively. Compared to the insulin solution, the C1 and C2 nanocomplexes significantly enhanced the permeation of insulin across the Caco-2 cell monolayers, with 6.36- and 4.05-fold increases in apparent permeability, respectively. Uptake mechanism studies were conducted using different endocytosis inhibitors and apical sodium-dependent bile acid transporter (ASBT)-transfected MDCK cells, which demonstrated the involvement of the energy-dependent ASBT-mediated active transport. Furthermore, the intrajejunal administration of C1 and C2 resulted in their pharmacological availabilities (PA) being 6.44% and 0.10%, respectively, indicating increased potential for C1, when compared to C2. Similarly, the PA and the relative bioavailability with intrajejunal administration of the C1 were 17.89-fold and 16.82-fold greater than those with intracolonic administration, respectively, confirming better jejunal absorption of C1. Overall, these findings indicate that the HIP-nanocomplexes could be a prominent platform for the effective delivery of peptides with improved intestinal absorption.

Modulatory Effect of Theaflavins on Apical Sodium-Dependent Bile Acid Transporter (ASBT) Activity.

Inhibiting apical sodium-dependent bile acid transporter (ASBT) has been identified as a potential strategy to reduce plasma cholesterol levels. Thus, in this study, we aimed to identify polyphenols that inhibited ASBT activity and to elucidate their mechanism. ASBT is responsible for most of the taurocholic acid (TC) uptake in Caco-2 cells. Of the 39 polyphenols examined, theaflavin (TF)-3-gallate (TF2A) and theaflavin-3'-gallate (TF2B) have been found to significantly reduce TC uptake in Caco-2 cells to 37.4 ± 2.8 and 33.8 ± 4.0%, respectively, of that in the untreated cells. The results from the TC uptake assay using N-acetylcysteine suggested that the inhibitory effect of TF2A and TF2B was attributed to the oxidization of their benzotropolone rings and their covalent bonding with ASBT's cysteine. TC uptake was reduced in the COS-7 cells expressing recombinant ASBT whose cysteine residues were mutated to alanine. Finally, the substrate concentration-dependent TC uptake assay showed that TFs competitively inhibited TC uptake.

Evaluation for Potential Drug-Drug Interaction of MT921 Using In Vitro Studies and Physiologically-Based Pharmacokinetic Models.

MT921 is a new injectable drug developed by Medytox Inc. to reduce submental fat. Cholic acid is the active pharmaceutical ingredient, a primary bile acid biosynthesized from cholesterol, endogenously produced by liver in humans and other mammals. Although individuals treated with MT921 could be administered with multiple medications, such as those for hypertension, diabetes, and hyperlipidemia, the pharmacokinetic drug–drug interaction (DDI) has not been investigated yet. Therefore, we studied in vitro against drug-metabolizing enzymes and transporters. Moreover, we predicted the potential DDI between MT921 and drugs for chronic diseases using physiologically-based pharmacokinetic (PBPK) modeling and simulation. The magnitude of DDI was found to be negligible in in vitro inhibition and induction of cytochrome P450s and UDP-glucuronosyltransferases. Organic anion transporting polypeptide (OATP)1B3, organic anion transporter (OAT)3, Na+-taurocholate cotransporting polypeptide (NTCP), and apical sodium-dependent bile acid transporter (ASBT) are mainly involved in MT921 transport. Based on the result of in vitro experiments, the PBPK model of MT921 was developed and evaluated by clinical data. Furthermore, the PBPK model of amlodipine was developed and evaluated. PBPK DDI simulation results indicated that the pharmacokinetics of MT921 was not affected by the perpetrator drugs. In conclusion, MT921 could be administered without a DDI risk based on in vitro study and related in silico simulation. Further clinical studies are needed to validate this finding.

Auxin transport mechanism of membrane transporter encoded by AEC gene of Bacillus licheniformis isolated from metagenome of Tapta Kund Hotspring of Uttrakhand, India

Members of group Bacillus are most widely occurring microbes in agricultural soil and they affect crop health in various ways. They directly stimulate plant growth either by augmenting nutrients availability, invigorating plants' defence mechanisms; repressing soil-borne phytopathogens or by producing growth-regulating hormones like auxins and cytokinins. It is a well known fact that indole-3- acetic acid (a type of auxin) is a vital biologically active phytohormone excreted by certain Bacillus species, but its molecular mechanism has not yet been described. In this study, the auxin efflux carrier gene is isolated from the metagenome of the Tapta Kund hot spring, Uttrakhand, India. In addition, auxin efflux carrier (AEC) transporter protein of Bacillus licheniformis is modeled and the 318 amino acid residues long protein was found homologous to the apical sodium-dependent bile acid transporter (ASBT) of Yersinia frederiksnii, with 10 transmembrane segments (TM1–10) split into different domains: a panel domain defined by TM1, 2, 6 and 7; and a core domain defined by TM3–5 and 8–10. Finally, the predicted Bacillus licheniformis AEC protein has also been phylogenetically evaluated and its detailed molecular transport mechanism was worked out using molecular dynamics simulation analysis. Conclusively, this study demonstrates the efflux mechanism of the substrate, Indole 3- acetic acid by AEC transporter protein.

Metformin impairs bile acid homeostasis in ethinylestradiol-induced cholestasis in mice

Metformin, an oral antidiabetic drug, recently demonstrated a reducing effect on bile acids (BA) plasma concentrations in one patient with intrahepatic cholestasis of pregnancy (ICP) by unknown mechanism. Therefore, the aim of the present study was to examine the effect of metformin on BA homeostasis and related molecular pathways in the liver and intestine using a mouse model of ICP. The cholestasis was induced in female C57BL/6 mice by repeated administration of ethinylestradiol (10 mg/kg BW s.c.) and/or metformin (150 mg/kg BW orally) over 5 consecutive days with subsequent bile collection and molecular analysis of samples. We demonstrated that metformin significantly increased the rate of bile secretion in control mice. This increase was BA dependent and was produced both by increased liver BA synthesis via induced cholesterol 7α-hydroxylase (Cyp7a1) and by increased BA reabsorption in the ileum via induction of the apical sodium-dependent BA transporter (Asbt). In contrast, metformin further worsened ethinylestradiol-induced impairment of bile secretion. This reduction was also BA dependent and corresponded with significant downregulation of Bsep, and Ntcp, major excretory and uptake transporters for BA in hepatocytes, respectively. The plasma concentrations of BA were consequently significantly increased in the metformin-treated mice. Altogether, our data indicate positive stimulation of bile secretion by metformin in the intact liver, but this drug also induces serious impairment of BA biliary secretion, with a marked increase in plasma concentrations in estrogen-induced cholestasis. Our results imply that metformin should be used with caution in situations with hormone-dependent cholestasis, such as ICP.

Targeting the Four Pillars of Enterohepatic Bile Salt Cycling; Lessons From Genetics and Pharmacology.

Bile salts play a pivotal role in lipid homeostasis, are sensed by specialized receptors, and have been implicated in various disorders affecting the gut or liver. They may play a role either as culprit or as potential panacea. Four very efficient transporters mediate most of the hepatic and intestinal bile salt uptake and efflux, and are each essential for the efficient enterohepatic circulation of bile salts. Starting from the intestinal lumen, conjugated bile salts cross the otherwise impermeable lipid bilayer of (primarily terminal ileal) enterocytes through the apical sodium–dependent bile acid transporter (gene SLC10A2) and leave the enterocyte through the basolateral heteromeric organic solute transporter, which consists of an alpha and beta subunit (encoded by SLC51A and SLC51B). The Na+‐taurocholate cotransporting polypeptide (gene SLC10A1) efficiently clears the portal circulation of bile salts, and the apical bile salt export pump (gene ABCB11) pumps the bile salts out of the hepatocyte into primary bile, against a very steep concentration gradient. Recently, individuals lacking either functional Na+‐taurocholate cotransporting polypeptide or organic solute transporter have been described, completing the quartet of bile acid transport deficiencies, as apical sodium–dependent bile acid transporter and bile salt export pump deficiencies were already known for years. Novel pathophysiological insights have been obtained from knockout mice lacking functional expression of these genes and from pharmacological transporter inhibition in mice or humans. Conclusion: We provide a concise overview of the four main bile salt transport pathways and of their status as possible targets of interventions in cholestatic or metabolic disorders.

Substrate Specificities and Inhibition Pattern of the Solute Carrier Family 10 Members NTCP, ASBT and SOAT.

Three carriers of the solute carrier family SLC10 have been functionally characterized so far. Na+/taurocholate cotransporting polypeptide NTCP is a hepatic bile acid transporter and the cellular entry receptor for the hepatitis B and D viruses. Its intestinal counterpart, apical sodium-dependent bile acid transporter ASBT, is responsible for the reabsorption of bile acids from the intestinal lumen. In addition, sodium-dependent organic anion transporter SOAT specifically transports sulfated steroid hormones, but not bile acids. All three carriers show high sequence homology, but significant differences in substrate recognition that makes a systematic structure-activity comparison attractive in order to define the protein domains involved in substrate binding and transport. By using stably transfected NTCP-, ASBT-, and SOAT-HEK293 cells, systematic comparative transport and inhibition experiments were performed with more than 20 bile acid and steroid substrates as well as different inhibitors. Taurolithocholic acid (TLC) was identified as the first common substrate of NTCP, ASBT and SOAT with K m values of 18.4, 5.9, and 19.3 µM, respectively. In contrast, lithocholic acid was the only bile acid that was not transported by any of these carriers. Troglitazone, BSP and erythrosine B were identified as pan-SLC10 inhibitors, whereas cyclosporine A, irbesartan, ginkgolic acid 17:1, and betulinic acid only inhibited NTCP and SOAT, but not ASBT. The HBV/HDV-derived myr-preS1 peptide showed equipotent inhibition of the NTCP-mediated substrate transport of taurocholic acid (TC), dehydroepiandrosterone sulfate (DHEAS), and TLC with IC50 values of 182 nM, 167 nM, and 316 nM, respectively. In contrast, TLC was more potent to inhibit myr-preS1 peptide binding to NTCP with IC50 of 4.3 µM compared to TC (IC50 = 70.4 µM) and DHEAS (IC50 = 52.0 µM). Based on the data of the present study, we propose several overlapping, but differently active binding sites for substrates and inhibitors in the carriers NTCP, ASBT, SOAT.

Gut-restricted apical sodium-dependent bile acid transporter inhibitor attenuates alcohol-induced liver steatosis and injury in mice.

Recent studies have shown that human and experimental alcohol-related liver disease (ALD) is robustly associated with dysregulation of bile acid homeostasis, which may in turn modulate disease severity. Pharmacological agents targeting bile acid metabolism and signaling may be potential therapeutics for ALD. The potential beneficial effects of a gut-restricted apical sodium-dependent bile acid transporter (ASBT) inhibitor were studied in a chronic-plus-binge ALD mouse model. Blocking intestinal bile acid reabsorption by the gut-restricted ASBT inhibitor GSK2330672 attenuated hepatic steatosis and liver injury in a chronic-plus-binge ALD mouse model. Alcohol feeding is associated with intestinal bile acid accumulation but paradoxically impaired ileal farnesoid×receptor (FXR) function, and repressed hepatic cholesterol 7α-hydrolase (CYP7A1) expression despite decreased hepatic small heterodimer partner (SHP) and ileal fibroblast growth factor 15 (FGF15) expression. ASBT inhibitor treatment decreased intestinal bile acid accumulation and increased hepatic CYP7A1 expression, but further decreased ileal FXR activity. Alcohol feeding induces serum bile acid concentration that strongly correlates with a liver injury marker. However, alcohol-induced serum bile acid elevation is not due to intrahepatic bile acid accumulation but is strongly and positively associated with hepatic multidrug resistance-associated protein 3 (MRP4) and MRP4 induction but poorly associated with sodium-taurocholate cotransporting peptide (NTCP) expression. ASBT inhibitor treatment decreases serum bile acid concentration without affecting hepatocyte basolateral bile acid uptake and efflux transporters. ASBT inhibitor treatment corrects alcohol-induced bile acid dysregulation and attenuates liver injury in experimental ALD.

Hepatitis D Virus Entry Inhibitors Based on Repurposing Intestinal Bile Acid Reabsorption Inhibitors.

Identification of Na+/taurocholate co-transporting polypeptide (NTCP) as high-affinity hepatic entry receptor for the Hepatitis B and D viruses (HBV/HDV) opened the field for target-based development of cell-entry inhibitors. However, most of the HBV/HDV entry inhibitors identified so far also interfere with the physiological bile acid transporter function of NTCP. The present study aimed to identify more virus-selective inhibitors of NTCP by screening of 87 propanolamine derivatives from the former development of intestinal bile acid reabsorption inhibitors (BARIs), which interact with the NTCP-homologous intestinal apical sodium-dependent bile acid transporter (ASBT). In NTCP-HEK293 cells, the ability of these compounds to block the HBV/HDV-derived preS1-peptide binding to NTCP (virus receptor function) as well as the taurocholic acid transport via NTCP (bile acid transporter function) were analyzed in parallel. Hits were subsequently validated by performing in vitro HDV infection experiments in NTCP-HepG2 cells. The most potent compounds S985852, A000295231, and S973509 showed in vitro anti-HDV activities with IC50 values of 15, 40, and 70 µM, respectively, while the taurocholic acid uptake inhibition occurred at much higher IC50 values of 24, 780, and 490 µM, respectively. In conclusion, repurposing of compounds from the BARI class as novel HBV/HDV entry inhibitors seems possible and even enables certain virus selectivity based on structure-activity relationships.

Deletion of Intestinal SHP Impairs Short-term Response to Cholic Acid Challenge in Male Mice.

Small heterodimer partner (SHP) is a crucial regulator of bile acid (BA) transport and synthesis; however, its intestine-specific role is not fully understood. Here, we report that male intestine-specific Shp knockout (IShpKO) mice exhibit higher intestinal BA but not hepatic or serum BA levels compared with the f/f Shp animals when challenged with an acute (5-day) 1% cholic acid (CA) diet. We also found that BA synthetic genes Cyp7a1 and Cyp8b1 are not repressed to the same extent in IShpKO compared with control mice post-CA challenge. Loss of intestinal SHP did not alter Fxrα messenger RNA (mRNA) but increased Asbt (BA ileal uptake transporter) and Ostα (BA ileal efflux transporter) expression even under chow-fed conditions. Surprisingly, the acute CA diet in IShpKO did not elicit the expected induction of Fgf15 but was able to maintain the suppression of Asbt, and Ostα/β mRNA levels. At the protein level, apical sodium-dependent bile acid transporter (ASBT) was downregulated, while organic solute transporter-α/β (OSTα/β) expression was induced and maintained regardless of diet. Examination of ileal histology in IShpKO mice challenged with acute CA diet revealed reduced villi length and goblet cell numbers. However, no difference in villi length, and the expression of BA regulator and transporter genes, was seen between f/f Shp and IShpKO animals after a chronic (14-day) CA diet, suggesting a potential adaptive response. We found the upregulation of the Pparα-Ugt axis after 14 days of CA diet may reduce the BA burden and compensate for the ileal SHP function. Thus, our study reveals that ileal SHP expression contributes to both overall intestinal structure and BA homeostasis.

Redox-responsive prodrug for improving oral bioavailability of paclitaxel through bile acid transporter-mediated pathway

Most anticancer drugs are not orally bioavailable due to their undesirable physicochemical properties and inherent physiological barriers. In this study, a polymeric prodrug strategy was presented to enhance the oral bioavailability of BCS class IV drugs using paclitaxel (PTX) as the model drug. PTX was covalently conjugated with cholic acid-functionalized PEG by a redox-sensitive disulfide bond. Cholic acid-functionalized PEGylated PTX (CPP) achieved remarkably improved PTX solubility (>30,000-fold), as well as favorable stability under the physiological environment and controlled drug release in the tumor. Meanwhile, CPP could self-assemble into nanoparticles with an average size of 56.18 ± 2.06 nm and drug loading up to 17.6% (w/w). Then, permeability study on Caco-2 cell monolayers demonstrated that CPP obtained an approximately 4-fold increase by apical sodium-dependent bile acid transporter (ASBT) mediated transport, compared with Taxol®. Pharmacokinetic studies carried out in rats confirmed that the oral bioavailability of CPP was 10-fold higher than that of Taxol®. Finally, significant improvement in the antitumor efficacy of CPP against breast cancer was confirmed on MDA-MB-231 cells. In summary, this prodrug-based cascade strategy offers new ways for chemotherapeutic drugs whose oral delivery is limited by solubility and permeability, also endows drugs with the capacity of tumor-specific release.

Identification of Triterpene Acids in Poria cocos Extract as Bile Acid Uptake Transporter Inhibitors.

Literature reports that Poria cocos reduces blood lipid levels; however, the underlying mechanism remains unclear. Blood lipid levels are closely related to the enterohepatic circulation of bile acids, where uptake transporters playing a significant role. P. cocos extract is commonly used in traditional prescriptions and food supplements in China. We investigated the effects of P. cocos and its five triterpene acids on bile acid uptake transporters, including intestinal apical sodium-dependent bile acid transporter (ASBT) and hepatic sodium/taurocholate cotransporting polypeptide (NTCP). Triterpene acids were fingerprinted by high-performance liquid chromatography-TripleTOF and quantified by ultraperformance liquid chromatography/tandem mass spectrometry. The inhibitory effect of P. cocos and its five major representative triterpene acids on ASBT and NTCP was investigated by in vitro assays using Xenopus oocytes expressing ASBT and NTCP. P. cocos extract exhibited significant inhibitory effects with half-maximum inhibition constants of 5.89 µg/ml and 14.6 µg/ml for NTCP and ASBT, respectively. Among five triterpene acids, poricoic acid A, poricoic acid B, and polyporenic acid C significantly inhibited NTCP function. Poricoic acid A, poricoic acid B, and dehydrotumulosic acid significantly inhibited ASBT function. The representative triterpene acid, poricoic acid A, was identified as a competitive inhibitor of NTCP with an inhibitory constant of 63.4 ± 18.7 µM. In conclusion, our results indicate that both P. cocos extract and its major triterpenes are competitive inhibitors of ASBT and NTCP. Accordingly, it was suggested that competitive inhibition of these bile acid transporters is one of the underlying mechanisms for the hypolipidemic effect of P. cocos. SIGNIFICANCE STATEMENT: Poria cocos, a commonly used Chinese herbal medicine and food supplement, demonstrates significantly inhibitory effects on the function of apical sodium-dependent bile acid transporter and sodium/taurocholate cotransporting polypeptide. P. cocos has potential to reduce the blood lipid through inhibition of these uptake transporters in enterohepatic circulation of bile acid.

Linderae Radix Ethanol Extract Alleviates Diet-Induced Hyperlipidemia by Regulating Bile Acid Metabolism Through gut Microbiota.

Hyperlipidemia is a common metabolic disorder and regarded as one of the main risk factors for cardiovascular disease. The gut microbiota has been identified as a potential contributor to hyperlipidemia as it can greatly regulate bile acid metabolism. Linderae radix is a natural medicine widely used in the treatment of a variety of diseases and is also a common drug for hyperlipidemia. Recently, the lipid-lowering effect of Linderae radix are receiving increasing attention but the underlying mechanism remains unknown. The study aimed to investigate the effects of Linderae radix ethanol extract (LREE) on gut microbiota in rats with hyperlipidemia syndrome. We established a hyperlipidemia rat model using a high-fat diet and used LREE as the intervention. Blood lipid levels and pathological examination were measured to assess the effects of LREE on hyperlipidemia. The gut microbiota was determined by 16s rDNA sequencing and the bile acid metabolism-related proteins were detected by western blot to discover the underlying correlations. The results show that LREE lowered TC, TG, and LDL levels effectively, and it also alleviated liver injury by reducing ALT and AST activity. Meanwhile, LREE improved gut microbiota disturbance caused by HFD via increasing intestinal microbiota diversity and changing the abundance of the Firmicutes, Bacteroidetes, and Actinobacteria. In addition, LREE can increase bile acid reabsorption and promote fecal excretion through farnesoid X receptor (FXR), apical sodium-dependent bile acid transporter (ASBT), organic solute transporter alpha (OST-α), and cytochrome P450 family 7 Subfamily A Member 1 (CYP7A1) thus restoring abnormal bile acid metabolism caused by hyperlipidemia.

MECHANISMS IN ENDOCRINOLOGY: FXR signalling: a novel target in metabolic diseases.

During the last decades, it has become clear that the gastrointestinal tract plays a pivotal role in the regulation of glucose homeostasis. More than 40 hormones originate from the gastrointestinal tract and several of these impact glucose metabolism and appetite regulation. An astonishing example of the gut's integrative role in glucose metabolism originates from investigations into bile acid biology. From primary animal studies, it has become clear that bile acids should no longer be labelled as simple detergents necessary for lipid digestion and absorption but should also be recognised as metabolic regulators implicated in lipid, glucose and energy metabolism. The nuclear farnesoid X receptor (FXR) is a part of an exquisite bile acid-sensing system that among other things ensures the optimal size of the bile acid pool. In addition, intestinal and hepatic FXR also impact the regulation of several metabolic processes such as glucose and lipid metabolism. Accordingly, natural and synthetic FXR agonists and certain FXR-regulated factors (i.e. fibroblast growth factor 19 (FGF19)) are increasingly being evaluated as treatments for metabolic diseases such as type 2 diabetes and non-alcoholic fatty liver disease (and its inflammatory version, non-alcoholic steatohepatitis). Interestingly, decreased FXR activation also benefits glucose metabolism. This can be obtained by reducing bile acid absorption using bile acid sequestering agents (approved for the treatment of type 2 diabetes) or inhibitors of intestinal bile acid transporters,that is the apical sodium-dependent bile acid transporter (ASBT). This article discusses recent clinical trials that provide insights about the role of FXR-FGF19-targetted therapy for the treatment of metabolic diseases.

Deoxycholic acid-functionalised nanoparticles for oral delivery of rhein

Rhein (RH) is a candidate for the treatment of kidney diseases. However, clinical application of RH is impeded by low aqueous solubility and oral bioavailability. Deoxycholic acid-conjugated nanoparticles (DNPs) were prepared by ionic interaction for enhancing intestinal absorption by targeting the apical sodium-dependent bile acid transporter in the small intestine. Resultant DNPs showed relatively high entrapment efficiency (90.7 ± 0.73)% and drug-loading efficiency (6.5 ± 0.29)% with a particle size of approximately 190 nm and good overall dispersibility. In vitro release of RH from DNPs exhibited sustained and pH-dependent profiles. Cellular uptake and apparent permeability coefficient (Papp) of the DNPs were 3.25- and 5.05-fold higher than that of RH suspensions, respectively. An in vivo pharmacokinetic study demonstrated significantly enhanced oral bioavailability of RH when encapsulated in DNPs, with 2.40- and 3.33-fold higher Cmax and AUC0-inf compared to RH suspensions, respectively. DNPs are promising delivery platforms for poorly absorbed drugs by oral administration.