Hydrophobic Bile Acids Research Articles

Downregulation of peroxiredoxin-3 by hydrophobic bile acid induces mitochondrial dysfunction and cellular senescence in human trophoblasts.

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy-specific disorder characterised by raised bile acids in foetal-maternal circulation, which threatens perinatal health. During the progression of ICP, the effect of oxidative stress is underscored. Peroxiredoxin-3 (PRDX3) is a mitochondrial antioxidant enzyme that is crucial to balance intracellular oxidative stress. However, the role of PRDX3 in placental trophoblast cells under ICP is not fully understood. We demonstrated that the level of PRDX3 was downregulated in ICP placentas as well as bile acids–treated trophoblast cells and villous explant in vitro. Toxic levels of bile acids and PRDX3 knockdown induced oxidative stress and mitochondrial dysfunction in trophoblast cells. Moreover, silencing of PRDX3 in trophoblast cell line HTR8/SVneo induced growth arrest and cellular senescence via activation of p38-mitogen-activated protein kinase (MAPK) and induction of p21WAF1/CIP and p16INK4A. Additionally, enhanced cellular senescence, determined by senescence-associated beta-galactosidase staining, was obviously attenuated by p38-MAPK inhibitor SB203580. Our data determined that exposure to bile acid decreased PRDX3 level in human trophoblasts. PRDX3 protected trophoblast cells against mitochondrial dysfunction and cellular senescence induced by oxidative stress. Our results suggest that decreased PRDX3 by excessive bile acids in trophoblasts plays a critical role in the pathogenesis and progression of ICP.

Ursodeoxycholic acid, in contrast to other bile acids, induces Ca2+-dependent cyclosporin A-insensitive permeability transition in liver mitochondria in the presence of potassium chloride

The effects of hydrophobic and hydrophilic bile acids as inducers of Ca2+-dependent permeability of the inner membrane were studied on isolated liver mitochondria. It is shown that in the absence of the inorganic phosphate (Pi)–a modulator of the mitochondrial pore–hydrophobic bile acids (lithocholic, deoxycholic, chenodeoxycholic) at concentrations of 20–50 μM, as well as a hydrophilic cholic acid at a concentration of 800 μM, induce swelling of liver mitochondria loaded with Ca2+. This effect is completely eliminated by a specific inhibitor of mitochondrial pore cyclosporin A (CsA). The effect of the bile acids as inducers of Ca2+-dependent CsA-sensitive mitochondrial pore is not associated with the modulation of the Pi effects. In contrast to other tested bile acids, a hydrophilic ursodeoxycholic acid (UDCA) at a concentration of 400 μM is able to induce Ca2+-dependent CsA-sensitive pore opening in liver mitochondria only in the presence of Pi or in the absence of potassium chloride in the incubation medium. In the presence of potassium chloride but in the absence of Pi, UDCA effects associated with the induction of the inner membrane permeability (swelling of mitochondria, drop in Δψ, and Ca2+ release from the matrix) are also observed in the presence of CsA. This Ca2+-dependent permeability of the inner membrane, in contrast to the “classical” CsA-sensitive pore, is characterized by a lower intensity of the mitochondrial swelling, a total drop in Δψ, and Ca2+ release from the matrix and is blocked by Pi. We suggest that the induction of the CsA-insensitive permeability in the inner mitochondrial membrane by UDCA is associated with activation of electrophoretic influx of K+ into the matrix and Ca2+ release from the matrix in exchange to H+. The effect of Pi as a blocker of such permeability is discussed.

Fibroblast growth factor 21 correlates with weight loss after vertical sleeve gastrectomy in adolescents.

Vertical sleeve gastrectomy (VSG) results in weight loss and increased bile acids (BA) and fibroblast growth factor 19 (FGF19) levels. FGF21 shares essential cofactors with FGF19, but its physiology early post-VSG has not been assessed. Ten adolescents (17.4 ± 0.5 years and BMI 51.5 ± 2.5 kg/m2 ) were enrolled. Fasting and postmeal (100 mL Ensure™) samples (0-120 min) were collected (pre-VSG [V1], 1 [V2], and 3 months [V3] post-VSG) for analysis of BA, FGF19, and FGF21. Post-VSG subjects lost weight (V2 11.8 ± 0.8 kg; V3 21.9 ± 1.7 kg). BA and FGF19 increased by V2, 143.6% at 30 min and 74.9% at 90 min post-meal, respectively. BA hydrophobicity index also improved by V3, 21.1% at 30 min post-meal. Interestingly, fasting and 120-min post-meal FGF21 levels at V2 were increased by 135.7% and 253.9%, respectively, but then returned to baseline at V3. BA levels correlated with FGF21 at V2 (P = 0.003, r = 0.89), and body weight lost post-VSG correlated with FGF21 levels (V2; P = 0.012, R = 0.82). Expected changes were seen in BA and FGF19 biology after VSG in adolescents, but novel changes were seen in correlation between the early postsurgical increase in FGF21 and weight loss, suggesting that FGF21 may play a role in energy balance postoperatively, and further investigation is warranted.

Obeticholic acid for the treatment of primary biliary cirrhosis

ABSTRACTIntroduction: There is significant unmet need in Primary Biliary Cholangitis (PBC) in patients under-responsive to the only approved therapy Ursodeoxycholic Acid (UDCA) who are at increased risk of progressing to end-stage liver disease. Obeticholic Acid (OCA) is a farnesoid X receptor (FXR) agonist which has been evaluated as a second line therapy in PBC and has recently been licenced by the FDA.Areas covered: The pharmacology and biology of OCA as an FXR agonist and its clinical benefits. A systematic review was undertaken of published literature, meeting abstracts and trial registries using the search terms FXR, FGF-19 (& FGF-15), Obeticholic Acid and INT-747.Expert commentary: OCA reduces exposure to toxic hydrophobic bile acids through reduction in bile acid synthesis (by direct and indirect (via enterocyte-released FGF19) actions on Cyp7A1-mediated bile acid synthesis) and bile acid excretion by hepatocytes. It significantly improves liver biochemical parameters strongly associated with risk of disease progression in UDCA under-responsive patients and the key side-effect of pruritus can be reduced by optimised dosing. OCA will be the first stratified therapy introduced in PBC, however confirmatory trial and real life data are needed to confirm that suggestive biochemical improvements are matched by improvement in key clinical outcomes.

Hydrophobic bile acids suppress expression of AE2 in biliary epithelial cells and induce bile duct inflammation in primary biliary cholangitis

Understanding the mechanisms of chronic inflammation in primary biliary cholangitis (PBC) is essential for successful treatment. Earlier work has demonstrated that patients with PBC have reduced expression of the anion exchanger 2 (AE2) on biliary epithelial cells (BEC) and deletion of AE2 gene has led to a PBC-like disorder in mice. To directly address the role of AE2 in preventing PBC pathogenesis, we took advantage of our ability to isolate human BEC and autologous splenic mononuclear cells (SMC). We studied the influence of hydrophobic bile acids, in particular, glycochenodeoxycholic acid (GCDC), on AE2 expression in BEC and the subsequent impact on the phenotypes of BEC and local inflammatory responses. We demonstrate herein that GCDC reduces AE2 expression in BEC through induction of reactive oxygen species (ROS), which enhances senescence of BEC. In addition, a reduction of AE2 levels by either GCDC or another AE2 inhibitor upregulates expression of CD40 and HLA-DR as well as production of IL-6, IL-8 and CXCL10 from BEC in response to toll like receptor ligands, an effect suppressed by inhibition of ROS. Importantly, reduced AE2 expression enhances the migration of autologous splenic mononuclear cells (SMC) towards BEC. In conclusion, our data highlight a key functional role of AE2 in the maintenance of the normal physiology of BEC and the pathogenic consequences of reduced AE2 expression, including abnormal intrinsic characteristics of BEC and their production of signal molecules that lead to the chronic inflammatory responses in small bile ducts.

Association between Circulating Vitamin D Metabolites and Fecal Bile Acid Concentrations

Although hydrophobic bile acids have been demonstrated to exhibit cytotoxic and carcinogenic effects in the colorectum, ursodeoxycholic acid (UDCA) has been investigated as a potential chemopreventive agent. Vitamin D has been shown to play a role in both bile acid metabolism and in the development of colorectal neoplasia. Using a cross-sectional design, we sought to determine whether baseline circulating concentrations of the vitamin D metabolites 25(OH)D and 1,25(OH)2D were associated with baseline fecal bile acid concentrations in a trial of UDCA for the prevention of colorectal adenoma recurrence. We also prospectively evaluated whether vitamin D metabolite concentrations modified the effect of UDCA on adenoma recurrence. After adjustment for age, sex, BMI, physical activity, and calcium intake, adequate concentrations of 25(OH)D (≥30 ng/mL) were statistically significantly associated with reduced odds for high levels of total [OR, 0.61; 95% confidence interval (CI), 0.38-0.97], and primary (OR, 0.61; 95% CI, 0.38-0.96) bile acids, as well as individually with chenodeoxycholic acid (OR, 0.39; 95% CI, 0.24-0.63) and cholic acid (OR, 0.56; 95% CI, 0.36-0.90). No significant associations were observed for 1,25(OH)2D and high versus low fecal bile acid concentrations. In addition, neither 25(OH)D nor 1,25(OH)2D modified the effect of UDCA on colorectal adenoma recurrence. In conclusion, this is the first study to demonstrate an inverse relationship between circulating levels of 25(OH)D and primary fecal bile acid concentrations. These results support prior data demonstrating that vitamin D plays a key role in bile acid metabolism, and suggest a potential mechanism of action for 25(OH)D in colorectal cancer prevention. Cancer Prev Res; 9(7); 589-97. ©2016 AACR.

Dysregulated hepatic bile acids collaboratively promote liver carcinogenesis.

Dysregulated bile acids (BAs) are closely associated with liver diseases and attributed to altered gut microbiota. Here, we show that the intrahepatic retention of hydrophobic BAs including deoxycholate (DCA), taurocholate (TCA), taurochenodeoxycholate (TCDCA), and taurolithocholate (TLCA) were substantially increased in a streptozotocin and high fat diet (HFD) induced nonalcoholic steatohepatitis-hepatocellular carcinoma (NASH-HCC) mouse model. Additionally chronic HFD-fed mice spontaneously developed liver tumors with significantly increased hepatic BA levels. Enhancing intestinal excretion of hydrophobic BAs in the NASH-HCC model mice by a 2% cholestyramine feeding significantly prevented HCC development. The gut microbiota alterations were closely correlated with altered BA levels in liver and feces. HFD-induced inflammation inhibited key BA transporters, resulting in sustained increases in intrahepatic BA concentrations. Our study also showed a significantly increased cell proliferation in BA treated normal human hepatic cell lines and a down-regulated expression of tumor suppressor gene CEBPα in TCDCA treated HepG2 cell line, suggesting that several hydrophobic BAs may collaboratively promote liver carcinogenesis.

Importance of detoxifying enzymes in differentiating fibrotic development between SHRSP5/Dmcr and SHRSP rats.

High-fat and -cholesterol diet (HFC) induced fibrotic steatohepatitis in stroke-prone spontaneously hypertensive rat (SHRSP) 5/Dmcr, the fifth substrain from SHRSP, by dysregulating bile acid (BA) kinetics. This study aimed to clarify the histopathological and BA kinetic differences in HFC-induced fibrosis between SHRSP5/Dmcr and SHRSP. Ten-week-old male SHRSP5/Dmcr and SHRSP were randomly allocated to groups and fed with either control diet or HFC for 2 and 8weeks. The liver histopathology, biochemical features, and molecular signaling involved in BA kinetics were measured. HFC caused more severe hepatocyte ballooning, macrovesicular steatosis and fibrosis in SHRSP5/Dmcr than in SHRSP. It was noted that fibrosis was disproportionately formed in retroperitoneal side of both strains. As for BA kinetics, HFC greatly increased the level of Cyp7a1 and Cyp7b1 to the same degree in both strains at 8weeks, while multidrug resistance-associated protein 3 was greater in SHRSP5/Dmcr than SHRSP. The diet decreased the level of bile salt export pump by the same degree in both strains, while constitutive androstane receptor, pregnane X receptor, and UDP-glucuronosyltransferase activity more prominent in SHRSP5/Dmcr than SHRSP at 8weeks. In the fibrosis-related genes, only expression of collagen, type I, alpha 1 mRNA was greater in SHRSP5/Dmcr than SHRSP. The greater progression of fibrosis in SHRSP5/Dmcr induced by HFC may be due to greater suppression of UDP-glucuronosyltransferase activity detoxifying toxicants, such as hydrophobic BAs.

Primary Bile Acid Chenodeoxycholic Acid-Based Microcapsules to Examine β-cell Survival and the Inflammatory Response

In past studies using hydrogel-polyelectrolyte matrix and different bile acid excipients, we microencapsulated pancreatic β-cells using various methods, and the microcapsules were mechanically stable, displayed good morphological characteristics with good physico-chemical compatibility but had limited cell viability and poor cell survival. Using bile acids, cell survival increased but overall remained limited. Thus, this study aimed to test different microencapsulating methods and examine the effects of the primary hydrophobic bile acid, chenodeoxycholic acid (CDCA), on β-cell microcapsules, in terms of morphology and cell function. Using the polymer sodium alginate (SA) and the co-polymer poly-l-ornithine (PLO), in 10:1 ratio, two microcapsules were made, one without CDCA and one with CDCA. During the microencapsulation process, polymer flow rate and culture media flow rate were screened (0.1–1.5 mL/min) for most uniform microcapsule. Pancreatic β-cells (NIT-1) were microencapsulated and tested for morphology, formulation physico-chemical compatibility, stability, surface topography and chemical composition. Encapsulated cell viability, metabolism, respiration, bioenergetics, biological activity and the inflammatory profile were also measured. A polymer flow rate of 0.8 mL/min accompanied by 0.6 mL/min media flow rate were found to produce the most uniform microcapsules using 10:1 formulation ratio. The microcapsules showed poor cell viability which was improved significantly after CDCA incorporation. CDCA also enhanced insulin secretion (p < 0.01), metabolism, respiration and bioenergetics (p < 0.01) and significantly reduced the inflammatory response. These benefits were attained without compromising microcapsule size or stability. A polymer flow rate of 0.8 mL/min and a media flow rate of 0.6 mL/min produced good microcapsules when using SA and PLO in 10:1 ratio, and the incorporation of the primary bile acid, chenodeoxycholic acid, enhanced microcapsule stability and significantly increased cell survival and reduced inflammation which suggests potential applications in β-cell microencapsulation and transplantation.

Hydrophobic bile acid apoptosis is regulated by sphingosine-1-phosphate receptor 2 in rat hepatocytes and human hepatocellular carcinoma cells.

The hepatotoxic bile acid glycochenodeoxycholate (GCDC) modulates hepatocyte cell death through activation of JNK, Akt, and Erk. The nonhepatotoxic bile acid taurocholate activates Akt and Erk through the sphingosine-1-phosphate receptor 2 (S1PR2). The role of the S1PR2 in GCDC-mediated apoptosis and kinase activation is unknown. Studies were done in rat hepatocytes, HUH7 cells, and HUH7 cells stably transfected with rat Ntcp (HUH7-Ntcp). Cells were treated with GCDC and apoptosis was monitored morphologically by Hoechst staining and biochemically by immunoblotting for the active cleaved fragment of caspase 3. Kinase activation was determined by immunoblotting with phospho-specific antibodies. JTE-013, an inhibitor of S1PR2, significantly attenuated morphological evidence of GCDC-induced apoptosis and prevented caspase 3 cleavage in rat hepatocytes and HUH7-Ntcp cells. In hepatocytes, JTE-013 mildly suppressed, augmented, and had no effect on GCDC-induced JNK, Akt, and Erk phosphorylation, respectively. Similar results were seen in HUH7-Ntcp cells except for mild suppression of JNK and Erk phosphorylation. Knockdown of S1PR2 in HUH7-Ntcp augmented Akt, inhibited JNK, and had no effect on Erk phosphorylation. GCDC failed to induce apoptosis or kinase activation in HUH7 cells. In conclusion, SIPR2 inhibition attenuates GCDC-induced apoptosis and inhibits and augments GCDC-induced JNK and Akt phosphorylation, respectively. In addition, GCDC must enter hepatocytes to mediate cell death or activate kinases. These results suggest that SIPR2 activation is proapoptotic in GCDC-induced cell death but that this effect is not due to direct ligation of the S1PR2 by the bile acid.

Hydrophobic bile acids relax rat detrusor contraction via inhibiting the opening of the Na⁺/Ca²⁺ exchanger.

Hydrophobic bile acids (BAs) are thought to inhibit smooth muscle contractility in several organs. The present study was undertaken to investigate the effects of hydrophobic BAs on the detrusor contractility of rat bladder and to explore the possible mechanism. Lithocholic acid (LCA) treatment increased the micturition interval and induced a concentration-dependent relaxation of bladder detrusor strips. In addition, LCA reduced the concentration of intracellular free Ca2+([Ca2+]i) and inhibited both the outward and inward Na+/Ca2+ exchanger (NCX) current (INCX) in primary isolated smooth muscle cells (SMCs). To further investigate the mechanism of action of LCA, several pharmacologic agents were used. We found that the NCX inhibitor 3′,4′-Dichlorobenzamil (DCB) can significantly inhibit the relaxation of detrusor strips and a reduction of the [Ca2+]i induced by LCA, while the antagonist of muscarinic receptor and the agonist of the G protein-coupled bile acid receptor (TGR5) and the farnesoid X receptor (FXR) had no effect. In conclusion, these data suggest that the relaxation of rat detrusor induced by hydrophobic BAs is mediated by NCX. Further research is needed to carry out to demonstrate the possible pathway and provide a potential new strategy to investigation for the treatment of the low urinary tract syndromes.

Microbiota and bile acid profiles in retinoic acid-primed mice that exhibit accelerated liver regeneration.

All-trans Retinoic acid (RA) regulates hepatic lipid and bile acid homeostasis. Similar to bile acid (BA), RA accelerates partial hepatectomy (PHx)-induced liver regeneration. Because there is a bidirectional regulatory relationship between gut microbiota and BA synthesis, we examined the effect of RA in altering the gut microbial population and BA composition and established their relationship with hepatic biological processes during the active phases of liver regeneration. C57BL/6 mice were treated with RA orally followed by 2/3 PHx. The roles of RA in shifting gut microbiota and BA profiles as well as hepatocyte metabolism and proliferation were studied. RA-primed mice exhibited accelerated hepatocyte proliferation revealed by higher numbers of Ki67-positive cells compared to untreated mice. Firmicutes and Bacteroidetes phyla dominated the gut microbial community (>85%) in both control and RA-primed mice after PHx. RA reduced the ratio of Firmicutes to Bacteroidetes, which was associated with a lean phenotype. Consistently, RA-primed mice lacked transient lipid accumulation normally found in regenerating livers. In addition, RA altered BA homeostasis and shifted BA profiles by increasing the ratio of hydrophilic to hydrophobic BAs in regenerating livers. Accordingly, metabolic regulators fibroblast growth factor 21, Sirtuin1, and their downstream targets AMPK and ERK1/2 were more robustly activated in RA-primed than unprimed regenerating livers. Priming mice with RA resulted in a lean microbiota composition and hydrophilic BA profiles, which were associated with facilitated metabolism and enhanced cell proliferation.

Deficiency of calcium-independent phospholipase A2 beta with aging causes biliary epithelial ductular reaction associated with increased bile acids in enterohepatic circulation

Background/Aims: Calcium-independent phospholipase A2 beta (iPLA2beta) generates lysophosphatidylcholine which is recognized as a macrophage 'fine me' signal for removal of apoptotic cells. We have shown that iPLA2beta deficiency causes an accumulation of apoptotic hepatocytes associated with a decrease of serum and hepatic lipids including cholesterol. We here determined whether iPLA2beta deficiency in aged mice can result in abnormalities in the hepatobiliary system and the alterations of bile acid contents. Methods: Control (WT) and whole body male iPLA2beta-/- mice at 19 – 22 months old were used. Bile acid profiles were measured by liquid-chromatography mass spectrometry. Functional assays included qRT-PCR, histology, and immunohistochemistry (IHC). Results: Livers of aged iPLA2beta-/- mice exhibited increased IHC staining of α-smooth muscle actin and biliary epithelial marker cytokeratin 19 compared with those of aged WT mice. This was concomitant with increases of total, hydrophilic, hydrophobic and secondary bile acids in the bile. The increases of hydrophobic secondary bile acids such as deoxycholic and chenodeoxycholic acids were observed in liver and intestine of iPLA2beta-/- mice, which was associated with increased mRNA expression of CYP7A1 and CYP8B1, and decreased expression of bile acid export genes BSEP and MRP3 in liver as well as OSTα and OSTβ in intestine. In the feces of mutant mice, we observed an increase of deoxycholic acid (suggesting increased dehydroxylation by luminal bacteria), but decreases of tauro-ursodeoxycholic acid as well as tauro- and glyco-chenodeoxycholic acids (suggesting increased deconjugation by luminal bacteria). Conclusions: iPLA2beta deficiency in aged mice caused biliary ductular expansion, and an accumulation of bile acids within enterohepatic circulation. This accumulation was a result of suppressed hepatic and intestinal bile acid export and increased bile acid syntheses, and the latter may lead to a decreased level of the bile acid precursor cholesterol. Thus, iPLA2beta plays a homeostatic role by regulating hepatic bile acid metabolism affecting systemic cholesterol levels and intestinal bile acid contents.

TGR5 knockout mice are highly susceptible to LCA induced liver damage

TGR5 (Gpbar-1) is a G-Protein-coupled membrane-bound cell surface-receptor for bile acids associated not only with the regulation of bile acid homeostasis, but also with the suppression of macrophage activity (1,2). It is expressed in several different organs and cell types, e.g. nonparenchymal liver cells and monocytes/macrophages. Thereby, TGR5 can function as a mediator for bile acids in modulating different pathologies of the liver distinguished by inflammatory processes (1,2). Lithocholic acid (LCA) is a hydrophobic bile acid with toxic properties produced by intestinal bacteria. Feeding of a diet containing 1% LCA leads to intrahepatic cholestasis, inflammation and toxic liver damage in mice (3,4). The role of TGR5 during this process is yet to be determined.

Transgenic overexpression of Niemann-Pick C2 protein promotes cholesterol gallstone formation in mice

Niemann-Pick C2 (NPC2) is a lysosomal protein involved in the egress of low-density lipoprotein-derived cholesterol from lysosomes to other intracellular compartments. NPC2 has been detected in several tissues and is also secreted from the liver into bile. We have previously shown that NPC2-deficient mice fed a lithogenic diet showed reduced biliary cholesterol secretion as well as cholesterol crystal and gallstone formation. This study aimed to investigate the consequences of NPC2 hepatic overexpression on liver cholesterol metabolism, biliary lipid secretion, gallstone formation and the effect of NPC2 on cholesterol crystallization in model bile. We generated NPC2 transgenic mice (Npc2.Tg) and fed them either chow or lithogenic diets. We studied liver cholesterol metabolism, biliary lipid secretion, bile acid composition and gallstone formation. We performed cholesterol crystallization studies in model bile using a recombinant NPC2 protein. No differences were observed in biliary cholesterol content or secretion between wild-type and Npc2.Tg mice fed the chow or lithogenic diets. Interestingly, Npc2.Tg mice showed an increased susceptibility to the lithogenic diet, developing more cholesterol gallstones at early times, but did not show differences in the bile acid hydrophobicity and gallbladder cholesterol saturation indices compared to wild-type mice. Finally, recombinant NPC2 decreased nucleation time in model bile. These results suggest that NPC2 promotes cholesterol gallstone formation by decreasing the cholesterol nucleation time, indicating a pro-nucleating function of NPC2 in bile.

A novel approach to the discovery of anti-tumor pharmaceuticals: searching for activators of liponecrosis

A recently conducted chemical genetic screen for pharmaceuticals that can extend longevity of the yeast Saccharomyces cerevisiae has identified lithocholic acid as a potent anti-aging molecule. It was found that this hydrophobic bile acid is also a selective anti-tumor chemical compound; it kills different types of cultured cancer cells if used at concentrations that do not compromise the viability of non-cancerous cells. These studies have revealed that yeast can be successfully used as a model organism for high-throughput screens aimed at the discovery of selectively acting anti-tumor small molecules. Two metabolic traits of rapidly proliferating fermenting yeast, namely aerobic glycolysis and lipogenesis, are known to be similar to those of cancer cells. The mechanisms underlying these key metabolic features of cancer cells and fermenting yeast have been established; such mechanisms are discussed in this review. We also suggest how a yeast-based chemical genetic screen can be used for the high-throughput development of selective anti-tumor pharmaceuticals that kill only cancer cells. This screen consists of searching for chemical compounds capable of increasing the abundance of membrane lipids enriched in unsaturated fatty acids that would therefore be toxic only to rapidly proliferating cells, such as cancer cells and fermenting yeast.

A novel, protective role of ursodeoxycholate in bile-induced pancreatic ductal injury.

We have previously shown that chenodeoxycholic acid (CDCA) strongly inhibits pancreatic ductal HCO3 (-) secretion through the destruction of mitochondrial function, which may have significance in the pathomechanism of acute pancreatitis (AP). Ursodeoxycholic acid (UDCA) is known to protect the mitochondria against hydrophobic bile acids and has an ameliorating effect on cell death. Therefore, our aim was to investigate the effect of UDCA pretreatment on CDCA-induced pancreatic ductal injury. Guinea pig intrainterlobular pancreatic ducts were isolated by collagenase digestion. Ducts were treated with UDCA for 5 and 24 h, and the effect of CDCA on intracellular Ca(2+) concentration ([Ca(2+)]i), intracellular pH (pHi), morphological and functional changes of mitochondria, and the rate of apoptosis were investigated. AP was induced in rat by retrograde intraductal injection of CDCA (0.5%), and the disease severity of pancreatitis was assessed by measuring standard laboratory and histological parameters. Twenty-four-hour pretreatment of pancreatic ducts with 0.5 mM UDCA significantly reduced the rate of ATP depletion, mitochondrial injury, and cell death induced by 1 mM CDCA and completely prevented the inhibitory effect of CDCA on acid-base transporters. UDCA pretreatment had no effect on CDCA-induced Ca(2+) signaling. Oral administration of UDCA (250 mg/kg) markedly reduced the severity of CDCA-induced AP. Our results clearly demonstrate that UDCA 1) suppresses the CDCA-induced pancreatic ductal injury by reducing apoptosis and mitochondrial damage and 2) reduces the severity of CDCA-induced AP. The protective effect of UDCA against hydrophobic bile acids may represent a novel therapeutic target in the treatment of biliary AP.

Dysregulation of bile acid homeostasis in parenteral nutrition mouse model.

Long-term parenteral nutrition (PN) administration can lead to PN-associated liver diseases (PNALD). Although multiple risk factors have been identified for PNALD, to date, the roles of bile acids (BAs) and the pathways involved in BA homeostasis in the development and progression of PNALD are still unclear. We have established a mouse PN model with IV infusion of PN solution containing soybean oil-based lipid emulsion (SOLE). Our results showed that PN altered the expression of genes involved in a variety of liver functions at the mRNA levels. PN increased liver gene expression of Cyp7a1 and markedly decreased that of Cyp8b1, Cyp7b1, Bsep, and Shp. CYP7A1 and CYP8B1 are important for synthesizing the total amount of BAs and regulating the hydrophobicity of BAs, respectively. Consistently, both the levels and the percentages of primary BAs as well as total non-12α-OH BAs increased significantly in the serum of PN mice compared with saline controls, whereas liver BA profiles were largely similar. The expression of several key liver-X receptor-α (LXRα) target genes involved in lipid synthesis was also increased in PN mouse livers. Retinoid acid-related orphan receptor-α (RORα) has been shown to induce the expression of Cyp8b1 and Cyp7b1, as well as to suppress LXRα function. Western blot showed significantly reduced nuclear migration of RORα protein in PN mouse livers. This study shows that continuous PN infusion with SOLE in mice leads to dysregulation of BA homeostasis. Alterations of liver RORα signaling in PN mice may be one of the mechanisms implicated in the pathogenesis of PNALD.

Relative contributions of L-FABP, SCP-2/SCP-x, or both to hepatic biliary phenotype of female mice

Both sterol carrier protein-2/sterol carrier protein-x (SCP-2/SCP-x) and liver fatty acid binding protein (L-FABP) have been proposed to function in hepatobiliary bile acid metabolism/accumulation. To begin to address this issue, the impact of ablating L-FABP (LKO) or SCP-2/SCP-x (DKO) individually or both together (TKO) was examined in female mice. Biliary bile acid levels were decreased in LKO, DKO, and TKO mice; however, hepatic bile acid concentration was decreased in LKO mice only. In contrast, biliary phospholipid level was decreased only in TKO mice, while biliary cholesterol levels were unaltered regardless of phenotype. The loss of either or both genes increased hepatic expression of the major bile acid synthetic enzymes (CYP7A1 and/or CYP27A1). Loss of L-FABP and/or SCP-2/SCP-x genes significantly altered the molecular composition of biliary bile acids, but not the proportion of conjugated/unconjugated bile acids or overall bile acid hydrophobicity index. These data suggested that L-FABP was more important in hepatic retention of bile acids, while SCP-2/SCP-x more broadly affected biliary bile acid and phospholipid levels.

Therapeutic and Chemopreventive Effects of Ursodeoxycholic Acid (UDCA): Potential Role in Patients with Barrett’s Esophagus

Ursodeoxycholic Acid (UDCA) is widely used for the treatment of cholestatic liver diseases. Major mechanisms of this action are protection of cholangiocytes against cytotoxicity of hydrophobic bile acids, stimulation of hepatobiliary secretion, and protection of hepatocytes against bile acid induced apoptosis. UDCA has also been shown to modulate mitochondrial transmembrane potential and prevent increases in mitochondrial Reactive Oxygen Species (ROS) production. Moreover, UDCA has been shown to have a chemopreventive role in mouse models of colon cancer and in patients with primary sclerosing cholangitis and concomitant In- flammatory Bowel Disease (IBD), low dose UDCA lowers the risk of IBD-associated colorec - tal neoplasia. Our studies suggest that oral UDCA may protect against DNA damage induced by hydrophobic bile acids such as Deoxycholic acid (DCA) in the metaplastic mucosa of patients with Barrett's esophagus. We have found that DCA induces carcinogenic DNA damage in Bar- rett's metaplasia. UDCA which counters the DNA damaging effects of DCA therefore might have a role as a chemopreventive agent in Barrett's metaplasia. Future clinical studies on the use of UDCA for chemoprevention in patients with Barrett's esophagus should be considered.