ABSTRACT
Apical sodium-dependent bile acid transporter （ASBT） is a key transporter responsible for intestinal reabsorption of bile acid and plays an important role in maintaining bile acid and cholesterol homeostasis， and its expression is regulated by various factors including transcription factors， nuclear receptors， and intestinal microflora. The abnormal expression and function of ASBT can lead to disorders in the metabolism of bile acid and cholesterol， causing a variety of hepatobiliary diseases. At present， ASBT has attracted wide attention as a therapeutic target. This article elaborates on the biological characteristics and expression regulation mechanism of ASBT and reviews the role of ASBT in hepatobiliary diseases， in order to provide a new direction for the treatment of related diseases.
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Bile acids (BAs) are a major component of bile salt, which plays a vital role in the metabolism of lipids in humans. Ninety-five percent of bile acids are recycled by the enterohepatic circulation (EHC), and therefore EHC is essential for bile acid homeostasis. There are four transporters that mediate the transmembrane transport of bile acids, each of which plays an important role in the enterohepatic circulation. Gene defects in bile acid transporters can lead to disorders of the enterohepatic circulation, ultimately leading to clinical phenotypes such as metabolic diseases and even death. Bile transporter expression is altered in patients with various metabolic disease states, suggesting that disruption of bile acid transporters may be a pivotal pathological mechanism for the development of metabolism diseases. Thus, many drugs targeting bile acid transporters are being developed. We provide a concise overview of the progress of bile acid transporters research, discuss the relationship between different bile acid transporters and disease development, and summarize the current progress in drug development targeting bile acid transporters.
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Orally administered drug entities have to survive the harsh gastrointestinal environment, penetrate the enteric epithelia and circumvent hepatic metabolism before reaching the systemic circulation. Whereas the gastrointestinal stability can be well maintained by taking proper measures, hepatic metabolism presents as a formidable barrier to drugs suffering from first-pass metabolism. The pharmaceutical academia and industries are seeking alternative pathways for drug transport to circumvent problems associated with the portal pathway. Intestinal lymphatic transport is emerging as a promising pathway to this end. In this review, we intend to provide an updated overview on the rationale, strategies, factors and applications involved in intestinal lymphatic transport. There are mainly two pathways for peroral lymphatic transport-the chylomicron and the microfold cell pathways. The underlying mechanisms are being unraveled gradually and nowadays witness increasing research input and applications.
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Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.
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BACKGROUND/AIMS: Cholangiocytes are capable of reabsorbing bile salts from bile, but the pathophysiological significance of this process is unclear. To this end, we detected the expression and distribution of bile acid transport proteins in cholangiocytes from normal rat liver and analyzed the possible pathophysiological significance. METHODS: Bile duct tissues of Sprague-Dawley rats were isolated by enzymatic digestion and mechanical isolation, and then divided into large and small bile duct tissues. Immunohistochemistry, real-time polymerase chain reaction and Western blotting were used to determine the expression of the apical sodium-dependent bile acid transporter (ASBT), ileal bile acid binding protein (IBABP), and basolateral organic solute transporter α (Ostα) in the biliary tract system of rats. Differences in the expression and distribution of these proteins were analyzed. RESULTS: In cholangiocytes, ASBT and IBABP were mainly expressed in cholangiocytes of the large bile ducts, in which the expression of both was significantly higher than that in the small ducts (p0.05). CONCLUSIONS: Bile acid transporters are expressed and heterogeneously distributed in rat bile ducts, indicating that bile acid reabsorption by cholangiocytes might mainly occur in the large bile ducts. These findings may help explore the physiology of bile ducts and the pathogenesis of various cholangiopathies.
Subject(s)
Animals , Rats , Bile Acids and Salts , Bile Ducts , Bile , Biliary Tract , Blotting, Western , Carrier Proteins , Digestion , Immunohistochemistry , Liver , Physiology , Population Characteristics , Rats, Sprague-Dawley , Real-Time Polymerase Chain ReactionABSTRACT
Objective To investigate the effect of sleeve gastrectomy (SG) on the distal ileum apical sodium-dependent bile acid transporter (ASBT) and ileum bile acid binding protein (IBABP)in obese type 2 diabetic rats.Methods Thirty 8-week-old male Sprague-Dawley rats were divided into groups O,F and N according to the random number table method.Among them,groups O and F were given high-sugar and high-fat diets,and group N were fed with normal diets before and after surgery.After 1,2 and 4 weeks,the body weight,blood glucose and plasma total bile acid levels were measured.The experimental animals were sacrificed 4 weeksafter operation and the terminal ileum tissue was harvested.Two types of ASBT and IABAP were detected by Western blot and immunohistochemistry.Bile acid transporters were tested.Results Blood glucose in group O was significantly lower than that in group F at 4 weeks postoperatively,(5.8±1.77) and (19.55±2.16) mmol/L,respectively (P＜0.05).Body weight in group O was significantly lower than that in group F at 4 weeks postoperatively,(182±10.66) g and (362±23.54) g,respectively (P＜0.05).Plasma total bile acid levels in group O were significantly higher than those in group F and N at 4 weeks after operation (52±18.48),(6.39±1.18),(5.89±1.21)μmol/L,respectively(P＜0.05).At the end of the 4th postoperative period,the expression of ASBT and IBABP in the distal ileum of group O increased,but there was no significant change in group F and group N.Conclusions The effect of SG on the hypoglycemic and weight-loss of obese T2DM rats is definite.The level of bile acid in plasma increases significantly after SG,and the expression of bile acid transporter in the terminal ileum of rats is one of the mechanisms.
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Bile acids play critical roles in the regulation of metabolism and absorption of lipids. The ileal apical sodium-dependent bile acid transporter (ASBT) located at the enterocyte brush border is responsible for the reuptake of bile acids and the maintenance of bile acid homeostasis. Recently, a number of investigations have been made concerning the regulation and control of ASBT and the relationship between ASBT and intestinal inflammation, tumorigenesis, diabetes mellitus and hyperlipemia, which suggests ASBT as a potential therapeutic target of these diseases. In this review, advances in the study of above-mentioned issues were summarized.
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This review focuses on various components of bile acid signaling in relation to cholangiocytes. Their roles as targets for potential therapies for cholangiopathies are also explored. While many factors are involved in these complex signaling pathways, this review emphasizes the roles of transmembrane G protein coupled receptor (TGR5), farnesoid X receptor (FXR), ursodeoxycholic acid (UDCA) and the bicarbonate umbrella. Following a general background on cholangiocytes and bile acids, we will expand the review and include sections that are most recently known (within 5-7 years) regarding the field of bile acid signaling and cholangiocyte function. These findings all demonstrate that bile acids influence biliary functions which can, in turn, regulate the cholangiocyte response during pathological events.
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The classical functions of bile acids include acting as detergents to facilitate the digestion and absorption of nutrients in the gut. In addition, bile acids also act as signaling molecules to regulate glucose homeostasis, lipid metabolism and energy expenditure. The signaling potential of bile acids in compartments such as the systemic circulation is regulated in part by an efficient enterohepatic circulation that functions to conserve and channel the pool of bile acids within the intestinal and hepatobiliary compartments. Changes in hepatobiliary and intestinal bile acid transport can alter the composition, size, and distribution of the bile acid pool. These alterations in turn can have significant effects on bile acid signaling and their downstream metabolic targets. This review discusses recent advances in our understanding of the inter-relationship between the enterohepatic cycling of bile acids and the metabolic consequences of signaling via bile acid-activated receptors, such as farnesoid X nuclear receptor (FXR) and the G-protein-coupled bile acid receptor (TGR5).
ABSTRACT
Bile acids play critical roles in the solubilization and absorption of lipids. The ileal apical sodium-dependent bile acid transporter( ASBT)located at the enterocyte brush border is responsible for the reuptake of bile acids and the maintenance of bile acid homeostasis. Recently,great success has been made in understanding the relationship between ASBT and intestinal inflammation,tumorigenesis,secretion,motility,sensation,gut microbiota,and gut-liver axis in addition to its expression regulation,which implicates ASBT as a contributor of some gastrointestinal diseases and a promising new therapeutic target for these diseases. In this review article,the advances in study on above-mentioned issues were summarized.
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BACKGROUND: Intrahepatic cholestasis can occur early after living donor liver transplantation (LDLT). We investigated the changes in the expressions of the bile acid transporters and the liver histology in the patients who suffered with early cholestasis (EC) following LDLT. METHODS: The histological differences between 15 graft livers with EC after LDLT and 5 graft livers with biliary stricture following LDLT were evaluated. The hepatic mRNA levels of the bile canaliculi transporters (BSEP, MRP2, MRP3, MDR1, MDR3, NTCP) in 40 (20 graft livers, 20 matched donor livers) liver biopsy tissues were analyzed by performing real-time reverse-transcription polymerase chain reaction (RT-PCR). RESULTS: Microscopic examination revealed hepatocellular and/or bile canalicular cholestasis around acinar zone 3 in the livers of the patients with EC. In the livers with biliary stricture, the cholestasis was dominantly observed in the hepatocytic cytoplasm and in the bile ductules around the portal area rather than around acinar zone 3. The BSEP and MRP2 mRNA levels in the EC livers were significantly reduced by 44% and 23%, respectively (p=0.000), compared to the matched donor livers. The levels of MDR3 and NTCP mRNA in the EC livers increased by 738% (p=0.000) and 281% (p<0.01), respectively. The change of the expressions of the bile acid transporters in the patients with biliary stricture was less significant than that in the EC group. CONCLUSIONS: These results suggest that the altered expressions of the bile acid transporters may play a role in the pathogenesis of EC following LDLT.
Subject(s)
Humans , Bile , Bile Canaliculi , Biopsy , Carrier Proteins , Cholestasis , Cholestasis, Intrahepatic , Constriction, Pathologic , Cytoplasm , Liver , Liver Transplantation , Living Donors , Membrane Glycoproteins , Polymerase Chain Reaction , RNA, Messenger , Tissue Donors , TransplantsABSTRACT
Objective To determine whether SC-435, a new ileal apical sodium-codependent bile acid transporter (IBAT) inhibitor, can alter the gastrointestinal motility in guinea pigs. Methods Sixty guinea pigs received regular diet or IBAT inhibitor (SC-435) diet for 2, 4, and 8 weeks, respectively. At the end of the feeding period, the gallbladder motility was assessed and then four bipolar silver electrodes were implanted on the antrum, duodenum, jejunum, and ileum. Seven days later, migrating motor complex (MMC) was recorded and the total bile acid pool size was measured according to the isotope dilution principle in the meantime. Results After feeding SC-435, the gallbla-dder motility was declined in the 4-week group and the 8-week group. The bile acid pool size decreased by 17.11% (P<0.05) in the 4-week group and 48.35% (P<0.05) in the 8-week group. The places of origin of MMC were changed where antral origins (37%) and duodenal origins (46%) decreased whereas jejunal origins (17%) increased. The MMC cycle period was prolonged in the duodenum (1.16 times in the 4-week group, P< 0.05; 1.38 times in the 8-week group, P<0.05) whereas MMC amplitude fell in the duodenum (10.58% in the 4-week group, P<0.05; 49.17% in the 8-week group, P<0.05). There were not significant differences in all parameters of MMC between the control group and the 2-week group in guinea pigs. Conclusion The IBAT inhibitor (SC-435) reduces the bile acid pool size and inhibits the MMC cycle activity. MMC is related to the enterohepatic circulation of bile acids, which is consistent with the changes of the bile acid pool size in guinea pigs.