Altered Bile Acid Homeostasis Research Articles

Abstract 2014: Ablation of LFABP (FABP1) leads to altered bile acid homeostasis and hyperplastic white adipose expansion

Abstract 2014: Ablation of LFABP (FABP1) leads to altered bile acid homeostasis and hyperplastic white adipose expansion

Development of a Humanized Mouse Model of Cholestatic Sickle Cell Disease

Sickle cell disease (SCD) is a group of autosomal recessive inherited disorders that affect approximately 100,000 people in the United States and millions worldwide. Liver or biliary complications including cirrhosis and cholestatic injury are evident in about 40% of hospitalized SCD patients. However, the molecular mechanisms responsible for sickle cell hepatopathy (SCH) remain poorly understood. Recently published studies and our preliminary data demonstrated impaired bile secretion and altered bile acid homeostasis accompanied red blood cell sequestration and fibrosis in the livers of humanized sickle cell mice. Although promising, a limitation of this model for the study of SCH is the predominance of hydrophilic bile acids in mice, which contrasts with a more hydrophobic and injurious bile acid pool in humans. A recent breakthrough in this area was the identification of murine-specific cytochrome P450 (Cyp2c70) as the enzyme responsible for the synthesis of mouse hydrophilic primary bile acids. Therefore, we hypothesize that the human hydrophobic bile acid composition would promote the development of cholestatic sickle cell disease. Methods:Tibias and femurs were excised from 2-month-old SCD SS and AA control mice and the bone marrow (BM) was collected. After lethal irradiation (2x 4.5Gy 4 hours apart), 2-month-old male recipient Cyp2c70-/- and their wildtype controls received BM-derived cells from either AA or SS mice. Cyp2c70-/- (KO) mice (C57Bl/6) were generated using CRISPR/Cas9 technology. Recipient Cyp2c70-/- and WTmice were reconstituted with SS and AA bone marrow and were euthanized 4 months after BMT. Standard growth parameters were recorded; liver, spleen, gallbladder bile, and blood were collected at necropsy for histologic, RNA, and chemical analyses. Results: Recipient Cyp2c70-/- (KO) SS mice had a significantly increased liver-to-body weight ratio compared to their controls. There was an increase in serum bile acids, direct bilirubin, and total bilirubin in SS recipient Cyp2c70-/- and WT mice compared to AA recipient mice. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were increased in Cyp2c70-/- (KO) overall with no observable difference in Cyp2c70-/- (KO) transplanted with AA or SS. An evaluation of liver histology by H&E revealed increased portal bridging and hepatic sequestration in sinusoids of recipient Cyp2c70-/- SS mice compared to control mice. Liver surface nodularity and morphological heterogeneity were also present in recipient Cyp2c70-/- SS mice compared to their controls. We observed increased collagen deposition as measured by Sirius Red staining in recipient Cyp2c70-/- SS mice compared to control mice. Liver histology revealed increased hepatic inflammation by F4/80 staining and bile duct proliferation by CK-19 and CK-8 staining in recipient Cyp2c70-/- SS mice. Conclusion: Coupled with the humanized sickle cell disease mouse, this novel sickle cell cholestatic liver mouse model can be used to investigate the role of hydrophobic bile acid-induced injury in sickle cell-related hepatobiliary disease and screen new therapeutic approaches for SCH. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Maternal obesogenic diet regulates offspring bile acid homeostasis and hepatic lipid metabolism via the gut microbiome in mice.

Mice exposed in gestation to maternal high-fat/high-sucrose (HF/HS) diet develop altered bile acid (BA) homeostasis. We hypothesized that these reflect an altered microbiome and asked if microbiota transplanted from HF/HS offspring change hepatic BA and lipid metabolism to determine the directionality of effect. Female mice were fed HF/HS or chow (CON) for 6 wk and bred with lean males. 16S sequencing was performed to compare taxa in offspring. Cecal microbiome transplantation (CMT) was performed from HF/HS or CON offspring into antibiotic-treated mice fed chow or high fructose. BA, lipid metabolic, and gene expression analyses were performed in recipient mice. Gut microbiomes from HF/HS offspring segregated from CON offspring, with increased Firmicutes to Bacteriodetes ratios and Verrucomicrobial abundance. After CMT was performed, HF/HS-recipient mice had larger BA pools, increased intrahepatic muricholic acid, and decreased deoxycholic acid species. HF/HS-recipient mice exhibited downregulated hepatic Mrp2, increased hepatic Oatp1b2, and decreased ileal Asbt mRNA expression. HF/HS-recipient mice exhibited decreased cecal butyrate and increased hepatic expression of Il6. HF/HS-recipient mice had larger livers and increased intrahepatic triglyceride versus CON-recipient mice after fructose feeding, with increased hepatic mRNA expression of lipogenic genes including Srebf1, Fabp1, Mogat1, and Mogat2. CMT from HF/HS offspring increased BA pool and shifted the composition of the intrahepatic BA pool. CMT from HF/HS donor offspring increased fructose-induced liver triglyceride accumulation. These findings support a causal role for vertical transfer of an altered microbiome in hepatic BA and lipid metabolism in HF/HS offspring.NEW & NOTEWORTHY We utilized a mouse model of maternal obesogenic diet exposure to evaluate the effect on offspring microbiome and bile acid homeostasis. We identified shifts in the offspring microbiome associated with changes in cecal bile acid levels. Transfer of the microbiome from maternal obesogenic diet-exposed offspring to microbiome-depleted mice altered bile acid homeostasis and increased fructose-induced hepatic steatosis.

NPC1L1 Deficiency Suppresses Ileal Fibroblast Growth Factor 15 Expression and Increases Bile Acid Pool Size in High-Fat-Diet-Fed Mice.

Niemann–Pick C1-like 1 (NPC1L1) mediates intestinal uptake of dietary and biliary cholesterol and is the target of ezetimibe, a cholesterol absorption inhibitor used to treat hypercholesterolemia. Genetic deletion of NPC1L1 or ezetimibe treatment protects mice from high-fat diet (HFD)-induced obesity; however, the molecular mechanisms responsible for this therapeutic benefit remain unknown. A major metabolic fate of cholesterol is its conversion to bile acids. We found that NPC1L1 knockout (L1-KO) mice fed an HFD had increased energy expenditure, bile acid pool size, and fecal bile acid excretion rates. The elevated bile acid pool in the HFD-fed L1-KO mice was enriched with tauro-β-muricholic acid. These changes in the L1-KO mice were associated with reduced ileal mRNA expression of fibroblast growth factor 15 (FGF15) and increased hepatic mRNA expression of cholesterol 7α-hydroxylase (Cyp7A1) and mitochondrial sterol 27-hydroxylase (Cyp27A1). In addition, mRNA expression of the membrane bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) and type 2 iodothyronine deiodinase (Dio2) were elevated in brown adipose tissue of L1-KO mice, which is known to promote energy expenditure. Thus, altered bile acid homeostasis and signaling may play a role in protecting L1-KO mice against HFD-induced obesity.

Novel Bile Acid-Dependent Mechanisms of Hepatotoxicity Associated with Tyrosine Kinase Inhibitors.

Drug-induced liver injury (DILI) is the leading cause of acute liver failure and a major concern in drug development. Altered bile acid homeostasis via inhibition of the bile salt export pump (BSEP) is one mechanism of DILI. Dasatinib, pazopanib, and sorafenib are tyrosine kinase inhibitors (TKIs) that competitively inhibit BSEP and increase serum biomarkers for hepatotoxicity in ∼25-50% of patients. However, the mechanism(s) of hepatotoxicity beyond competitive inhibition of BSEP are poorly understood. This study examined mechanisms of TKI-mediated hepatotoxicity associated with altered bile acid homeostasis. Dasatinib, pazopanib, and sorafenib showed bile acid-dependent toxicity at clinically relevant concentrations, based on the C-DILI assay using sandwich-cultured human hepatocytes (SCHH). Among several bile acid-relevant genes, cytochrome P450 (CYP) 7A1 mRNA was specifically upregulated by 6.2- to 7.8-fold (dasatinib) and 5.7- to 9.3-fold (pazopanib), compared with control, within 8 hours. This was consistent with increased total bile acid concentrations in culture medium up to 2.3-fold, and in SCHH up to 1.4-fold, compared with control, within 24 hours. Additionally, protein abundance of sodium taurocholate co-transporting polypeptide (NTCP) was increased up to 2.0-fold by these three TKIs. The increase in NTCP protein abundance correlated with increased function; dasatinib and pazopanib increased hepatocyte uptake clearance (CLuptake) of taurocholic acid, a probe bile acid substrate, up to 1.4-fold. In conclusion, upregulation of CYP7A1 and NTCP in SCHH constitute novel mechanisms of TKI-associated hepatotoxicity. SIGNIFICANCE STATEMENT: Understanding the mechanisms of hepatotoxicity associated with tyrosine kinase inhibitors (TKIs) is fundamental to development of effective and safe intervention therapies for various cancers. Data generated in sandwich-cultured human hepatocytes, an in vitro model of drug-induced hepatotoxicity, revealed that TKIs upregulate bile acid synthesis and alter bile acid uptake and excretion. These findings provide novel insights into additional mechanisms of bile acid-mediated drug-induced liver injury, an adverse effect that limits the use and effectiveness of TKI treatment in some cancer patients.

CYP3A deficiency alters bile acid homeostasis and leads to changes in hepatic susceptibility in rats

Cytochrome P450 3A (CYP3A) as an important enzyme metabolizes many drugs and a variety of endogenous substances. Bile acids (BA) regulate physiological function by activating BA receptors. In this study, CYP3A1/2 gene knockout (KO) and wild-type (WT) rats were used to investigate the regulatory effects of CYP3A on BA homeostasis and liver function. Compared with WT rats, BA concentrations in serum, liver and small intestine of CYP3A1/2 KO rats increased significantly, which was due to the decrease of catabolism and the increase of synthesis. In particular, the composition of serum BA (overall hydrophobicity) presented an age- and CYP3A-dependent manner. With the aging of WT rats, the serum BA became more hydrophobic, while this trend was delayed in CYP3A1/2 KO rats. Moreover, the level of serum total cholesterol, the precursor of BA synthesis, decreased by about 20% in CYP3A1/2 KO rats, which is due to the low synthesis but high biotransformation rate. The increase of BA pool further led to the change of transcription level of BA receptor in liver (pregnane X receptor) and small intestine (Takeda G-protein receptor 5), and affected the function and morphology of CYP3A1/2 KO rat liver. In conclusion, CYP3A is a key regulator of BA homeostasis in rats, especially in regulating BA pool size, composition and balance of anabolism, and prevents susceptibility to hepatotoxicity under BA overload.

Human-relevant mechanisms and risk factors for TAK-875-Induced liver injury identified via a gene pathway-based approach in Collaborative Cross mice

Development of TAK-875 was discontinued when a small number of serious drug-induced liver injury (DILI) cases were observed in Phase 3 clinical trials. Subsequent studies have identified hepatocellular oxidative stress, mitochondrial dysfunction, altered bile acid homeostasis, and immune response as mechanisms of TAK-875 DILI and the contribution of genetic risk factors in oxidative response and mitochondrial pathways to the toxicity susceptibility observed in patients. We tested the hypothesis that a novel preclinical approach based on gene pathway analysis in the livers of Collaborative Cross mice could be used to identify human-relevant mechanisms of toxicity and genetic risk factors at the level of the hepatocyte as reported in a human genome-wide association study. Eight (8) male mice (4 matched pairs) from each of 45 Collaborative Cross lines were treated with a single oral (gavage) dose of either vehicle or 600 mg/kg TAK-875. As expected, liver injury was not detected histologically and few changes in plasma biomarkers of hepatotoxicity were observed. However, gene expression profiling in the liver identified hundreds of transcripts responsive to TAK-875 treatment across all strains reflecting alterations in immune response and bile acid homeostasis and the interaction of treatment and strain reflecting oxidative stress and mitochondrial dysfunction. Fold-change expression values were then used to develop pathway-based phenotypes for genetic mapping which identified candidate risk factor genes for TAK-875 toxicity susceptibility at the level of the hepatocyte. Taken together, these findings support our hypothesis that a gene pathway-based approach using Collaborative Cross mice could inform sensitive strains, human-relevant mechanisms of toxicity, and genetic risk factors for TAK-875 DILI. This novel preclinical approach may be helpful in understanding, predicting, and ultimately preventing clinical DILI for other drugs.

ENDOCRINOLOGY IN PREGNANCY: Metabolic impact of bile acids in gestation.

Bile acids are lipid-solubilising molecules that also regulate metabolic processes. Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) are two bile acid receptors with key metabolic roles. FXR regulates bile acid synthesis in the liver and influences bile acid uptake in the intestine. TGR5 is mainly involved in regulation of signalling pathways in response to bile acid uptake in the gut and therefore prandial response. Both FXR and TGR5 have potential as therapeutic targets for disorders of glucose and/or lipid homeostasis. Gestation is also known to cause small increases in bile acid concentrations, but physiological hypercholanaemia of pregnancy is usually not sufficient to cause any clinically relevant effects. This review focuses on how gestation alters bile acid homeostasis, which can become pathological if the elevation of maternal serum bile acids is more marked than physiological hypercholanaemia, and on the influence of FXR and TGR5 function in pregnancy on glucose and lipid metabolism. This will be discussed with reference to two gestational disorders: intrahepatic cholestasis of pregnancy (ICP), a disease where bile acids are pathologically elevated, and gestational diabetes mellitus (GDM), characterised by hyperglycaemia during pregnancy.

Impact of Maternal Obesogenic Diet on Offspring Bile Acid Homeostasis and Disease Progression in Non‐Alcoholic Fatty Liver Disease is Transmitted to Next Generation by Male Offspring

BackgroundNon‐alcoholic fatty liver disease (NAFLD) affects approximately one‐quarter of the global population, with up to 20–25% developing progressive liver disease. Recent evidence in both humans and animal models show that maternal obesity is a risk factor for the development of NAFLD and progression to NASH. We have shown in a murine model of maternal obesity the offspring develop altered bile acid homeostasis and a varied response to a western diet which is passed by female offspring across generations. In this study we tested the hypothesis that male offspring exposed to maternal obesogenic diet pass an altered bile acid homeostasis phenotype and susceptibility to western diet induced liver disease to their offspring.MethodsFemale C57Bl6 mice were fed chow (CON) or HF/HS diet for 6 weeks to induce obesity and bred with lean males. Male F1 offspring were then bred with lean females to create a paternal second generation (PF2C from maternal CON lineage, PF2H from maternal HF/HS lineage). Tissues were collected from PF2 offspring to measure bile acid pool size and hepatic bile acid species profile. Additional PF2 offspring were fed high trans‐fat, cholesterol, fructose (HTFC) diet for 16 weeks to induce progressive NAFLD. Metabolic and histopathologic analyses were performed.ResultsIn chow fed PF2 offspring from the maternal HF/HS (mHF/HS) lineage, total BA pool size was increased. No change in intrahepatic BA composition was observed. After HTFC diet, PF2H offspring showed decreased liver weight and liver weight to body weight ratio compared to PF2C offspring. PF2H offspring exhibited lower levels of intrahepatic triglyceride and free fatty acids. Conversely, PF2H offspring liver showed increased Sirius red staining.ConclusionsMale offspring exposed to maternal obesogenic diet transmit a phenotype of altered BA homeostasis to their offspring. After exposure to a western diet, PF2H offspring exhibited worse fibrosis despite having less steatosis. Passage of these phenotypes through male offspring would suggest an epigenetic phenomenon as a mechanistic etiology. Future studies will evaluate the mechanism for transmission of maternal obesity driven changes in the liver across generations in the male lineage.

Mechanisms of Altered Bile Acid Homeostasis in Offspring Exposed to Maternal Obesogenic Diet

BackgroundNon‐alcoholic fatty liver disease (NAFLD) affects approximately one‐quarter of the global population with increasing prevalence in the pediatric population. There is currently no standard medical therapy and no diagnostic study capable of predicting which patients will develop severe disease. Recent evidence in both humans and animal models show that maternal obesity is a risk factor for the development of NAFLD and progression to NASH. We have shown in a murine model of maternal obesity the offspring develop periportal fibrosis and inflammation with associated changes in bile acid (BA) homeostasis. In this study we define the mechanisms of changes in BA homeostasis.MethodsFemale C57Bl6 mice were fed chow (CON) or HF/HS diet for 6 weeks to induce obesity and bred with lean males. Offspring were fed chow diet from the time of weaning until tissue collection. BA pool size and levels of specific intrahepatic bile acid species were measured. RT‐PCR was performed to evaluate gene expression of factors involved in bile acid metabolism and signaling. 16S sequencing was performed for evaluation of offspring microbiome. Levels of stool BAs were quantified and timed BA excretion performed.ResultsOffspring from the maternal HF/HS (mHF/HS) lineage exhibited an increase in total BA pool size with associated changes in expression of genes involved in bile acid metabolism (increased Cyp7a1, Cyp27a1). Measurement of specific bile acids in liver showed a shift in the intrahepatic BA pool composition (decreased deoxycholic acid, increased muricholic acid) in offspring from the mHF/HS lineage. Decreased BA excretion was observed in mHF/HS lineage offspring. Fecal microbiome analysis showed a decrease in alpha diversity and shifts in the abundance of particular phyla (increased Bacteroidetes, decreased Proteobacteria) and genera (increased Barnesiella, decreased Clostridium). Measurement of cecal BA levels showed an increase in abundance of muricholic acid (FXR antagonist) and a decrease in abundance of deoxycholic acid (FXR agonist) in mHF/HS lineage offspring.ConclusionsMaternal HF/HS diet exposure leads to pathologic changes in the offspring including periportal fibrosis and inflammation, which is associated with changes in BA homeostasis. Several factors are involved in the BA homeostasis changes including BA metabolism and excretion. Vertical transmission of gut dysbiosis may be a primary factor in driving changes in BA homeostasis in offspring exposed to maternal obesogenic diet.

Uremic solutes modulate hepatic bile acid handling and induce mitochondrial toxicity

Chronic kidney disease (CKD) is accompanied by accumulating levels of uremic solutes in the circulation. Changes in the size and composition of the bile acid pool have also been observed. We investigated via which mechanisms uremic solutes may interfere with hepatocyte function and thus contribute to altered bile acid handling. We studied interference on the level of bile acid synthesis by cytochrome P450 7A1 (CYP7A1), explored effects on hepatic bile acid transporters, and investigated effects on mitochondrial function. In HEK293 cells overexpressing bile salt transporters, we observed that p-cresyl sulfate inhibited Na+-taurocholate cotransporting polypeptide (NTCP)-mediated uptake of taurocholic acid (TCA), whereas organic anion-transporting polypeptide 1B1 (OATP1B1)-mediated TCA uptake was increased. Assays in transporter-overexpressing membrane vesicles revealed that kynurenic acid inhibited TCA transport via the bile salt efflux pump (BSEP), whereas p-cresyl glucuronide and hippuric acid increased TCA efflux via multidrug resistance-associated protein 3 (MRP3). Moreover, indoxyl sulfate decreased mRNA expression of NTCP, OATP1B3 and CYP7A1 in primary human hepatocytes. Transport studies confirmed a decreased TCA uptake in indoxyl sulfate-exposed hepatocytes. Decreased hepatocyte viability was found for all seven uremic solutes tested, whereas five out of seven also decreased intracellular ATP levels and mitochondrial membrane potential. In conclusion, uremic solutes affect hepatic bile acid transport and mitochondrial function. This can contribute to the altered bile acid homeostasis observed in CKD patients.

Pharmacological Activation of PXR and CAR Downregulates Distinct Bile Acid-Metabolizing Intestinal Bacteria and Alters Bile Acid Homeostasis.

The gut microbiome regulates important host metabolic pathways including xenobiotic metabolism and intermediary metabolism, such as the conversion of primary bile acids (BAs) into secondary BAs. The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are well-known regulators for xenobiotic biotransformation in liver. However, little is known regarding the potential effects of PXR and CAR on the composition and function of the gut microbiome. To test our hypothesis that activation of PXR and CAR regulates gut microbiota and secondary BA synthesis, 9-week-old male conventional and germ-free mice were orally gavaged with corn oil, PXR agonist PCN (75 mg/kg), or CAR agonist TCPOBOP (3 mg/kg) once daily for 4 days. PCN and TCPOBOP decreased two taxa in the Bifidobacterium genus, which corresponded with decreased gene abundance of the BA-deconjugating enzyme bile salt hydrolase. In liver and small intestinal content of germ-free mice, there was a TCPOBOP-mediated increase in total, primary, and conjugated BAs corresponding with increased Cyp7a1 mRNA. Bifidobacterium, Dorea, Peptociccaceae, Anaeroplasma, and Ruminococcus positively correlated with T-UDCA in LIC, but negatively correlated with T-CDCA in serum. In conclusion, PXR and CAR activation downregulates BA-metabolizing bacteria in the intestine and modulates BA homeostasis in a gut microbiota-dependent manner.

Fasiglifam (TAK-875) Alters Bile Acid Homeostasis in Rats and Dogs: A Potential Cause of Drug Induced Liver Injury.

Fasiglifam (TAK-875), a Free Fatty Acid Receptor 1 (FFAR1) agonist in development for the treatment of type 2 diabetes, was voluntarily terminated in phase 3 due to adverse liver effects. A mechanistic investigation described in this manuscript focused on the inhibition of bile acid (BA) transporters as a driver of the liver findings. TAK-875 was an in vitro inhibitor of multiple influx (NTCP and OATPs) and efflux (BSEP and MRPs) hepatobiliary BA transporters at micromolar concentrations. Repeat dose studies determined that TAK-875 caused a dose-dependent increase in serum total BA in rats and dogs. Additionally, there were dose-dependent increases in both unconjugated and conjugated individual BAs in both species. Rats had an increase in serum markers of liver injury without correlative microscopic signs of tissue damage. Two of 6 dogs that received the highest dose of TAK-875 developed liver injury with clinical pathology changes, and by microscopic analysis had portal granulomatous inflammation with neutrophils around a crystalline deposition. The BA composition of dog bile also significantly changed in a dose-dependent manner following TAK-875 administration. At the highest dose, levels of taurocholic acid were 50% greater than in controls with a corresponding 50% decrease in taurochenodeoxycholic acid. Transporter inhibition by TAK-875 may cause liver injury in dogs through altered bile BA composition characteristics, as evidenced by crystalline deposition, likely composed of test article, in the bile duct. In conclusion, a combination of in vitro and in vivo evidence suggests that BA transporter inhibition could contribute to TAK-875-mediated liver injury in dogs.

Disrupted Murine Gut-to-Human Liver Signaling Alters Bile Acid Homeostasis in Humanized Mouse Liver Models.

The humanized liver mouse model is being exploited increasingly for human drug metabolism studies. However, its model stability, intercommunication between human hepatocytes and mouse nonparenchymal cells in liver and murine intestine, and changes in extrahepatic transporter and enzyme expressions have not been investigated. We examined these issues in FRGN [fumarylacetoacetate hydrolase (Fah-/-), recombination activating gene 2 (Rag2-/-), and interleukin 2 receptor subunit gamma (IL-2rg -/-) triple knockout] on nonobese diabetic (NOD) background] and chimeric mice: mFRGN and hFRGN (repopulated with mouse or human hepatocytes, respectively). hFRGN mice showed markedly higher levels of liver cholesterol, biliary bilirubin, and bile acids (liver, bile, and plasma; mainly human forms, but also murine bile acids) but lower transforming growth factor beta receptor 2 (TGFBR2) mRNA expression levels (10%) in human hepatocytes and other proliferative markers in mouse nonparenchymal cells (Tgf-β1) and cholangiocytes [plasma membrane-bound, G protein-coupled receptor for bile acids (Tgr5)], suggestive of irregular regeneration processes in hFRGN livers. Changes in gene expression in murine intestine, kidney, and brain of hFRGN mice, in particular, induction of intestinal farnesoid X receptor (Fxr) genes: fibroblast growth factor 15 (Fgf15), mouse ileal bile acid binding protein (Ibabp), small heterodimer partner (Shp), and the organic solute transporter alpha (Ostα), were observed. Proteomics revealed persistence of remnant murine proteins (cyotchrome P450 7α-hydroxylase (Cyp7a1) and other enzymes and transporters) in hFRGN livers and suggest the likelihood of mouse activity. When compared with normal human liver tissue, hFRGN livers showed lower SHP mRNA and higher CYP7A1 (300%) protein expression, consequences of tβ- and tα-muricholic acid-mediated inhibition of the FXR-SHP cascade and miscommunication between intestinal Fgf15 and human liver fibroblast growth factor receptor 4 (FGFR4), as confirmed by the unchanged hepatic pERK/total ERK ratio. Dysregulation of hepatocyte proliferation and bile acid homeostasis in hFRGN livers led to hepatotoxicity, gallbladder distension, liver deformity, and other extrahepatic changes, making questionable the use of the preparation for drug metabolism studies.

Impaired Bile Acid Homeostasis in Children with Severe Acute Malnutrition.

ObjectiveSevere acute malnutrition (SAM) is a major cause of mortality in children under 5 years and is associated with hepatic steatosis. Bile acids are synthesized in the liver and participate in dietary fat digestion, regulation of energy expenditure, and immune responses. The aim of this work was to investigate whether SAM is associated with clinically relevant changes in bile acid homeostasis.DesignAn initial discovery cohort with 5 healthy controls and 22 SAM-patients was used to identify altered bile acid homeostasis. A follow up cohort of 40 SAM-patients were then studied on admission and 3 days after clinical stabilization to assess recovery in bile acid metabolism. Recruited children were 6–60 months old and admitted for SAM in Malawi. Clinical characteristics, feces and blood were collected on admission and prior to discharge. Bile acids, 7α-hydroxy-4-cholesten-3-one (C4) and FGF-19 were quantified.ResultsOn admission, total serum bile acids were higher in children with SAM than in healthy controls and glycine-conjugates accounted for most of this accumulation with median and interquartile range (IQR) of 24.6 μmol/L [8.6–47.7] compared to 1.9 μmol/L [1.7–3.3] (p = 0.01) in controls. Total serum bile acid concentrations did not decrease prior to discharge. On admission, fecal conjugated bile acids were lower and secondary bile acids higher at admission compared to pre- discharge, suggesting increased bacterial conversion. FGF19 (Fibroblast growth factor 19), a marker of intestinal bile acid signaling, was higher on admission and was associated with decreased C4 concentrations as a marker of bile acid synthesis. Upon recovery, fecal calprotectin, a marker of intestinal inflammation, was lower.ConclusionSAM is associated with increased serum bile acid levels despite reduced synthesis rates. In SAM, there tends to be increased deconjugation of bile acids and conversion from primary to secondary bile acids, which may contribute to the development of liver disease.

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.

Systems pharmacology modeling predicts delayed presentation and species differences in bile acid-mediated troglitazone hepatotoxicity.

Troglitazone (TGZ) caused delayed, life-threatening drug-induced liver injury (DILI) in some patients, but was not hepatotoxic in rats. This study investigated altered bile acid (BA) homeostasis as a mechanism of TGZ hepatotoxicity using a systems pharmacology model incorporating drug/metabolite disposition, BA physiology/pathophysiology, hepatocyte life cycle, and liver injury biomarkers. In the simulated human population, TGZ (200–600mg/day×6months) resulted in delayed increases in serum ALT>3× ULN in 0.3–5.1% of the population with concomitant bilirubin elevations>2× ULN in 0.3–3.6%. In contrast, pioglitazone (15–45mg/day×6months) did not elicit hepatotoxicity, consistent with clinical data. TGZ was not hepatotoxic in the simulated rat population. In summary, mechanistic modeling based only on BA effects accurately predicted the incidence, delayed presentation, and species differences in TGZ hepatotoxicity, and the relative liver safety of pioglitazone. Systems pharmacology models integrating physiology and experimental data can evaluate DILI mechanisms and may be useful to predict hepatotoxic potential of drug candidates.

An updated review on drug-induced cholestasis: Mechanisms and investigation of physicochemical properties and pharmacokinetic parameters

Drug-induced cholestasis is an important form of acquired liver disease and is associated with significant morbidity and mortality. Bile acids are key signaling molecules, but they can exert toxic responses when they accumulate in hepatocytes. This review focuses on the physiological mechanisms of drug-induced cholestasis associated with altered bile acid homeostasis due to direct (e.g., bile acid transporter inhibition) or indirect (e.g., activation of nuclear receptors, altered function/expression of bile acid transporters) processes. Mechanistic information about the effects of a drug on bile acid homeostasis is important when evaluating the cholestatic potential of a compound, but experimental data often are not available. The relationship between physicochemical properties, pharmacokinetic parameters, and inhibition of the bile salt export pump among 77 cholestatic drugs with different pathophysiological mechanisms of cholestasis (i.e., impaired formation of bile vs. physical obstruction of bile flow) was investigated. The utility of in silico models to obtain mechanistic information about the impact of compounds on bile acid homeostasis to aid in predicting the cholestatic potential of drugs is highlighted. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:3037–3057, 2013

Organic anion-transporting polypeptide 1a4 (Oatp1a4) is important for secondary bile acid metabolism

Organic anion transporting polypeptides (human: OATPs; rodent: Oatps) were thought to have important functions in bile acid (BA) transport. Oatp1a1, 1a4, and 1b2 are the three major Oatp1 family members in rodent liver. Our previous studies have characterized the BA homeostasis in Oatp1a1-null and Oatp1b2-null mice. The present study investigated the physiological role of Oatp1a4 in BA homeostasis by using Oatp1a4-null mice. Oatp1a4 expression is female-predominant in livers of mice, and thereby it was expected that female Oatp1a4-null mice will have more prominent changes than males. Interestingly, the present study demonstrated that female Oatp1a4-null mice had no significant alterations in BA concentrations in serum or liver, though they had increased mRNA of hepatic BA efflux transporters (Mrp4 and Ostα/β) and ileal BA transporters (Asbt and Ostα/β). In contrast, male Oatp1a4-null mice showed significantly altered BA homeostasis, including increased concentrations of deoxycholic acid (DCA) in serum, liver and intestinal contents. After feeding a DCA-supplemented diet, male but not female Oatp1a4-null mice had higher concentrations of DCA in serum and livers than their WT controls. This suggested that Oatp1a4 is important for intestinal absorption of secondary BAs in male mice. Furthermore, loss of Oatp1a4 function did not decrease BA accumulation in serum or livers of bile-duct-ligated mice, suggesting that Oatp1a4 is not likely a BA uptake transporter. In summary, the present study for the first time demonstrates that Oatp1a4 does not appear to mediate the hepatic uptake of BAs, but plays an important male-predominant role in secondary BA metabolism in mice.

CLA-Enriched Diet Containing t10,c12- CLA Alters Bile Acid Homeostasis and Increases the Risk of Cholelithiasis in Mice

Mice fed a mixture of CLA containingt10,c12-CLA lose fat mass and develop hyperinsulinemia and hepatic steatosis due to an accumulation of TG and cholesterol. Because cholesterol is the precursor in bile acid (BA) synthesis, we investigated whethert10,c12-CLA alters BA metabolism. In Expt. 1, female C57Bl/6J mice were fed a standard diet for 28 d supplemented with a CLA mixture (1 g/100 g) or not (controls). In Expt. 2, the feeding period was reduced to 4, 6, and 10 d. In Expt. 3, mice were fed a diet supplemented with linoleic acid,c9,t11-CLA, ort10,c12-CLA (0.4 g/100 g) for 28 d. In Expt. 1, the BA pool size was greater in CLA-fed mice than in controls and the entero-hepatic circulation of BA was altered due to greater BA synthesis and ileal reclamation. This resulted from higher hepatic cholesterol 7a-hydroxylase (CYP7A1) and ileal apical sodium BA transporter expressions in CLA-fed mice. Furthermore, hepatic Na+/taurocholate co-transporting polypeptide (NTCP) (-52%) and bile salt export pump (BSEP) (-77%) protein levels were lower in CLA-fed mice than in controls, leading to a greater accumulation of BA in the plasma (+500%); also, the cholesterol saturation index and the concentration of hydrophobic BA in the bile were greater in CLA-fed mice, changes associated with the presence of cholesterol crystals. Expt. 2 suggests that CLA-mediated changes were caused by hyperinsulinemia, which occurred after 6 d of the CLA diet before NTCP and BSEP mRNA downregulation (10 d). Expt. 3 demonstrated that onlyt10,c12-CLA altered NTCP and BSEP mRNA levels. In conclusion,t10,c12-CLA alters BA homeostasis and increases the risk of cholelithiasis in mice.