Dose-response of five bile acids on serum and liver bile Acid concentrations and hepatotoxicty in mice

The profile of bile acids and their sulfate metabolites in human urine and serum

The role of sulfation in ameliorating the hepatotoxicity of bile acids (BAs) in humans remains unknown due to the lack of proper analytical methods to quantify individual BAs and their sulfate metabolites in biological tissues and fluids. To this end, a simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to characterize the detailed BA profile in human urine and serum. The limit of quantification was 1ng/mL and baseline separation of all analytes was achieved within in a run time of 32min. The method was validated over the dynamic range of 1-1000ng/mL. The LC-MS/MS method was more accurate, precise, and selective than the commercially available kits for the quantification of sulfated and unsulfated BAs, and the indirect quantification of individual sulfated BAs after solvolysis. The LC-MS/MS method was applied to characterize the BA profile in urine and serum of healthy subjects. Thirty three percent of serum BAs were sulfated, whereas 89% of urinary BAs existed in the sulfate form, indicating the role of sulfation in enhancing the urinary excretion of BAs. The percentage of sulfation of individual BAs increased with the decrease in the number of hydroxyl groups indicating the role of sulfation in the detoxification of the more hydrophobic and toxic BA species. Eighty percent of urinary BAs and 55% of serum BAs were present in the glycine-amidated form, whereas 8% of urinary BAs and 13% of serum BAs existed in the taurine-amidated form.

The receptor TGR5 protects the liver from bile acid overload during liver regeneration in mice

Many regulatory pathways are involved in liver regeneration after partial hepatectomy (PH) to initiate growth, protect liver cells, and sustain functions of the remnant liver. Bile acids (BAs), whose levels rise in the blood early after PH, stimulate both hepatocyte proliferation and protection, in part through their binding to the nuclear farnesoid X receptor (FXR). However, the effect of the BA receptor, TGR5 (G-protein-coupled BA receptor 1) after PH remains to be studied. Liver histology, hepatocyte proliferation, BA concentrations (plasma, bile, liver, urine, and feces), bile flow and composition, and cytokine production were studied in wild-type (WT) and TGR5 KO (knockout) mice before and after PH. BA composition (plasma, bile, liver, urine, and feces) was more hydrophobic in TGR5 KO than in WT mice. After PH, severe hepatocyte necrosis, prolonged cholestasis, exacerbated inflammatory response, and delayed regeneration were observed in TGR5 KO mice. Although hepatocyte adaptive response to post-PH BA overload was similar in WT and TGR5 KO mice, kidney and biliary adaptive responses were strongly impaired in TGR5 KO mice. Cholestyramine treatment, as well as Kupffer cell depletion, significantly improved the post-PH TGR5 KO mice phenotype. After bile duct ligation or upon a cholic acid-enriched diet, TGR5 KO mice exhibited more severe liver injury than WT as well as impaired BA elimination in urine.

CONCLUSION

TGR5 is crucial for liver protection against BA overload after PH, primarily through the control of bile hydrophobicity and cytokine secretion. In the absence of TGR5, intrahepatic stasis of abnormally hydrophobic bile and excessive inflammation, in association with impaired bile flow adaptation and deficient urinary BA efflux, lead to BA overload-induced liver injury and delayed regeneration.

IL-17A synergistically enhances bile acid-induced inflammation during obstructive cholestasis

During obstructive cholestasis, increased concentrations of bile acids activate ERK1/2 in hepatocytes, which up-regulates early growth response factor 1, a key regulator of proinflammatory cytokines, such as macrophage inflammatory protein 2 (MIP-2), which, in turn, exacerbates cholestatic liver injury. Recent studies have indicated that IL-17A contributes to hepatic inflammation during obstructive cholestasis, suggesting that bile acids and IL-17A may interact to regulate hepatic inflammatory responses. We treated mice with an IL-17A neutralizing antibody or control IgG and subjected them to bile duct ligation. Neutralization of IL-17A prevented up-regulation of proinflammatory cytokines, hepatic neutrophil accumulation, and liver injury, indicating an important role for IL-17A in neutrophilic inflammation during cholestasis. Treatment of primary mouse hepatocytes with taurocholic acid (TCA) increased the expression of MIP-2. Co-treatment with IL-17A synergistically enhanced up-regulation of MIP-2 by TCA. In contrast to MIP-2, IL-17A did not affect up-regulation of Egr-1 by TCA, indicating that IL-17A does not affect bile acid-induced activation of signaling pathways upstream of early growth response factor 1. In addition, bile acids increased expression of IL-23, a key regulator of IL-17A production in hepatocytes in vitro and in vivo. Collectively, these data identify bile acids as novel triggers of the IL-23/IL-17A axis and suggest that IL-17A promotes hepatic inflammation during cholestasis by synergistically enhancing bile acid-induced production of proinflammatory cytokines by hepatocytes.

Decreased hepatotoxic bile acid composition and altered synthesis in progressive human nonalcoholic fatty liver disease

Bile acids (BAs) have many physiological roles and exhibit both toxic and protective influences within the liver. Alterations in the BA profile may be the result of disease induced liver injury. Nonalcoholic fatty liver disease (NAFLD) is a prevalent form of chronic liver disease characterized by the pathophysiological progression from simple steatosis to nonalcoholic steatohepatitis (NASH). The hypothesis of this study is that the 'classical' (neutral) and 'alternative' (acidic) BA synthesis pathways are altered together with hepatic BA composition during progression of human NAFLD. This study employed the use of transcriptomic and metabolomic assays to study the hepatic toxicologic BA profile in progressive human NAFLD. Individual human liver samples diagnosed as normal, steatosis, and NASH were utilized in the assays. The transcriptomic analysis of 70 BA genes revealed an enrichment of downregulated BA metabolism and transcription factor/receptor genes in livers diagnosed as NASH. Increased mRNA expression of BAAT and CYP7B1 was observed in contrast to decreased CYP8B1 expression in NASH samples. The BA metabolomic profile of NASH livers exhibited an increase in taurine together with elevated levels of conjugated BA species, taurocholic acid (TCA) and taurodeoxycholic acid (TDCA). Conversely, cholic acid (CA) and glycodeoxycholic acid (GDCA) were decreased in NASH liver. These findings reveal a potential shift toward the alternative pathway of BA synthesis during NASH, mediated by increased mRNA and protein expression of CYP7B1. Overall, the transcriptomic changes of BA synthesis pathway enzymes together with altered hepatic BA composition signify an attempt by the liver to reduce hepatotoxicity during disease progression to NASH.

Bile acid-induced expression of farnesoid X receptor as the basis for superiority of internal biliary drainage in experimental biliary obstruction

AIMS AND OBJECTIVES

The aim is to determine the efficacy of internal and external biliary drainage (ED) with special reference to the effect of bile acid on intestinal epithelium during experimental biliary obstruction. Methods. A total of 59 male Sprague Dawley rats were randomly assigned to four groups: (I) sham operation (SH); (II) obstructive jaundice (OJ); (III) OJ and ED; and (IV) OJ and internal biliary drainage (ID). The animals underwent surgical ligation of the bile duct on day 1. They were reoperated on day 8 for biliary drainage procedure. Blood cultures were obtained from portal vein and inferior vena cava on day 15. Samples were also drawn for serum total bile acid (TBA) and white blood cell (WBC) counts. The terminal ileum was harvested to study the tight junction-associated protein ("occludin") and bile acid receptor ("farnesoid X receptor" [FXR]) using immunohistochemical method.

RESULTS

Serum TBA (118.9 ± 39.0 μmol/L) and WBC (11.4 ± 2.7 × 10(9)/L) were significantly increased (p = 0.001) after bile duct ligation as compared with SH rats (38.0 ± 15.0 μmol/L and 5.5 ± 1.0 × 10(9)/L, respectively; p = 0.001). The resulting mucosal lesion was high grade and the expressions of FXR and Occludin were decreased. After ED, there was slight decrease in total WBCs, whereas TBA levels declined significantly. The expression of FXR was minimal and Occludin showed no change (ED vs. OJ: p = 0.533). However, both WBC and TBA decreased after ID. The ileal structure, grade of mucosal lesion, and expression of FXR/Occludin were comparable with SH group (p > 0.05). The rate of bacterial translocation was: 57.1% (OJ); 62.5% (ID); and 80% (ED) with identical strains in cultures from the portal vein and inferior vena cava.

CONCLUSION

Downregulation of TBA/FXR expression during biliary obstruction results in damage to intestinal epithelium. Unlike ED, ID restores FXR/Occludin expression in the terminal ileum through reappearance of intestinal bile acid, which thus appears to be a key factor in maintaining integrity of the epithelial barrier.

Eicosapentaenoic acid attenuates hepatic accumulation of cholesterol esters but aggravates liver injury and inflammation in mice fed a cholate-supplemented high-fat diet

The administration of a sodium cholate-supplemented high-fat (CAHF) diet in mice induced the predominant accumulation of cholesterol esters (CE) in the liver and biochemical and histological features of liver injury. Cholesteryl oleate was the most abundant CE found in the liver of the mice fed the CAHF diet. We examined the effect of ethyl eicosapentaenoate (EPA) on hepatic CE accumulation and liver injury in the mice fed the CAHF diet. The EPA supplementation suppressed the elevation in the level of cholesteryl oleate in the liver. The expression levels of sterol O-acyltransferase-2 and stearoyl-CoA desaturase-1 mRNA in the liver were elevated in the mice fed the CAHF diet, but they were normalized by the EPA supplementation. However, the elevation in serum transaminase activity, the sign of inflammatory cell exudation and inflammatory gene responses in the liver of the mice fed the EPA-supplemented diet were enhanced compared with those of the mice fed the CAHF diet. We demonstrated that EPA supplementation attenuated CE accumulation but aggravated liver injury and liver inflammation in the mice fed the CAHF diet.

Effects of nuclear receptor transactivation on boar taint metabolism and gene expression in porcine hepatocytes

The accumulation of the testicular steroid androstenone (AND) and tryptophan degradation product skatole (3MI) in fat results in boar taint, an off odor and flavor in boar meat. Increasing boar taint metabolism in the liver may help limit the deposition of AND and 3MI in fat, thereby improving meat quality. The effects of transactivation of the nuclear receptors constitutive androstane receptor (CAR), pregnane X receptor (PXR), and farnesoid X receptor (FXR) on the expression levels of several transcripts of interest and the metabolism of AND and 3MI in primary porcine hepatocytes were tested. Primary cells were isolated from mature boars, and transcript expression levels were assayed using real-time PCR. The transcripts of interest included porcine orthologs of common phase I and phase II metabolic enzymes and transcripts previously shown to be differentially expressed in boars with high boar taint levels. Transactivation of CAR, PXR, or FXR resulted in altered expression of several transcripts, including increased expression of cytochrome P450 (CYP) 2B22 by CAR, of CYP2A19, CYP2B22, CYP2C33, and CYP2C49 by PXR, of CYP2C33 and CYP2E1 by FXR, and of CYP19A2 by all three receptors. Only transactivation of PXR had a significant effect on AND metabolism, resulting in 7.5±1.5% of the initial level of AND remaining compared to 21.4±3.1% remaining with control dimethyl sulfoxide (DMSO) treatment. FXR had the greatest effect on 3MI metabolism, increasing the expression of CYP2E1 by 1.29-fold and increasing the production of the key metabolite 6-hydroxy-3-methylindole (6-OH-3MI), while decreasing 5-hydroxy-3-methylindole (5-OH-3MI) production. 3-Hydroxy-3-methyloxindole (HMOI) production was increased by CAR transactivation, while indol-3-carbinol (I3C) production was increased by PXR and FXR transactivation, and by treatment with 5β-dihydrotestosterone (5β-DHT). From this, it can be concluded that selective transactivation of PXR and FXR may be a viable means of decreasing boar taint by increasing the hepatic metabolism of AND and 3MI.

Assessment of benzene-induced hematotoxicity using a human-like hematopoietic lineage in NOD/Shi-scid/IL-2Rγnull mice

Despite recent advancements, it is still difficult to evaluate in vivo responses to toxicants in humans. Development of a system that can mimic the in vivo responses of human cells will enable more accurate health risk assessments. A surrogate human hematopoietic lineage can be established in NOD/Shi-scid/IL-2Rγ^null (NOG) mice by transplanting human hematopoietic stem/progenitor cells (Hu-NOG mice). Here, we first evaluated the toxic response of human-like hematopoietic lineage in NOG mice to a representative toxic agent, benzene. Flow cytometric analysis showed that benzene caused a significant decrease in the number of human hematopoietic stem/progenitor cells in the bone marrow and the number of human leukocytes in the peripheral blood and hematopoietic organs. Next, we established chimeric mice by transplanting C57BL/6 mouse-derived bone marrow cells into NOG mice (Mo-NOG mice). A comparison of the degree of benzene-induced hematotoxicity in donor-derived hematopoietic lineage cells within Mo-NOG mice indicated that the toxic response of Hu-NOG mice reflected interspecies differences in susceptibilities to benzene. Responses to the toxic effects of benzene were greater in lymphoid cells than in myeloid cells in Mo-NOG and Hu-NOG mice. These findings suggested that Hu-NOG mice may be a powerful in vivo tool for assessing hematotoxicity in humans, while accounting for interspecies differences.

The bile salt export pump (BSEP) in health and disease

The bile salt export pump (BSEP) is the major transporter for the secretion of bile acids from hepatocytes into bile in humans. Mutations of BSEP are associated with cholestatic liver diseases of varying severity including progressive familial intrahepatic cholestasis type 2 (PFIC-2), benign recurrent intrahepatic cholestasis type 2 (BRIC-2) and genetic polymorphisms are linked to intrahepatic cholestasis of pregnancy (ICP) and drug-induced liver injury (DILI). Detailed analysis of these diseases has considerably increased our knowledge about physiology and pathophysiology of bile secretion in humans. This review focuses on expression, localization, and function, short- and long-term regulation of BSEP as well as diseases association and treatment options for BSEP-associated diseases.

Metabolomics reveals an essential role for peroxisome proliferator-activated receptor α in bile acid homeostasis

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor that regulates fatty acid transport and metabolism. Previous studies revealed that PPARα can affect bile acid metabolism; however, the mechanism by which PPARα regulates bile acid homeostasis is not understood. In this study, an ultraperformance liquid chromatography coupled with electrospray ionization qua dru pole time-of-flight mass spectrometry (UPLC-ESI-QTOFMS)-based metabolomics approach was used to profile metabolites in urine, serum, and bile of wild-type and Ppara-null mice following cholic acid (CA) dietary challenge. Metabolomic analysis showed that the levels of several serum bile acids, such as CA (25-fold) and taurocholic acid (16-fold), were significantly increased in CA-treated Ppara-null mice compared with CA-treated wild-type mice. Phospholipid homeostasis, as revealed by decreased serum lysophos phati dylcholine (LPC) 16:0 (1.6-fold) and LPC 18:0 (1.6-fold), and corticosterone metabolism noted by increased urinary excretion of 11β-hydroxy-3,20-dioxopregn-4-en-21-oic acid (20-fold) and 11β,20α-dihydroxy-3-oxo-pregn-4-en-21-oic acid (3.6-fold), were disrupted in CA-treated Ppara-null mice. The hepatic levels of mRNA encoding transporters Abcb11, Abcb4, Abca1, Abcg5, and Abcg8 were diminished in Ppara-null mice, leading to the accumulation of bile acids in the liver during the CA challenge. These observations revealed that PPARα is an essential regulator of bile acid biosynthesis, transport, and secretion.

Gender-divergent profile of bile acid homeostasis during aging of mice

Aging is a physiological process with a progressive decline of adaptation and functional capacity of the body. Bile acids (BAs) have been recognized as signaling molecules regulating the homeostasis of glucose, lipid, and energy. The current study characterizes the age-related changes of individual BA concentrations by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in serum and liver of male and female C57BL/6 mice from 3 to 27 months of age. Total BA concentrations in serum increased 340% from 3 to 27 months in female mice, whereas they remained relatively constant with age in male mice. During aging, male and female mice shared the following changes: (1) BA concentrations in liver remained relatively constant; (2) the proportions of beta-muricholic acid (βMCA) increased and deoxycholic acid (DCA) decreased between 3 and 27 months in serum and liver; and (3) total BAs in serum and liver became more hydrophilic between 3 and 27 months. In female mice, (1) the mRNAs of hepatic BA uptake transporters, the Na⁺/taurocholate cotransporting polypeptide (Ntcp) and the organic anion transporting polypeptide 1b2 (Oatp1b2), decreased after 12 months, and similar trends were observed for their proteins; (2) the mRNA of the rate-limiting enzyme for BA synthesis, cholesterol 7α-hydroxylase (Cyp7a1), increased from 3 to 9 months and remained high thereafter. However, in male mice, Ntcp, Oatp1b2, and Cyp7a1 mRNAs remained relatively constant with age. In summary, the current study shows gender-divergent profiles of BA concentrations and composition in serum and liver of mice during aging, which is likely due to the gender-divergent expression of BA transporters Ntcp and Oatp1b2 as well as the synthetic enzyme Cyp7a1.

TUDCA slows retinal degeneration in two different mouse models of retinitis pigmentosa and prevents obesity in Bardet-Biedl syndrome type 1 mice

PURPOSE

To evaluate and compare the protective effect of tauroursodeoxycholic acid (TUDCA) on photoreceptor degeneration in different models of retinal degeneration (RD) in mice.

METHODS

Bbs(M390R/M390R) mice were injected subcutaneously twice a week, from P40 to P120, and rd10 mice were injected every 3 days from P6 to P38 with TUDCA or vehicle (0.15 M NaHCO(3)). Rd1 and rd16 mice were injected daily from P6 to P30 with TUDCA or vehicle. Retinal structure and function were determined at multiple time points by electroretinography (ERG), optical coherence tomography (OCT), and histology.

RESULTS

The amplitude of ERG b-waves was significantly higher in TUDCA-treated Bbs1 and rd10 animals than in controls. Retinal thickness on OCT was slightly greater in treated Bbs1 animals than in the controls. Histologically, outer segments were preserved, and the outer nuclear layer was significantly thicker in the treated Bbs1 and rd10 mice than in the controls. Bbs1(M390R/M390R) mice developed less obesity than the control Bbs1(M390R/M390R) while receiving TUDCA. The Rd1 and rd16 mice showed no improvement with TUDCA treatment, and the rd1 mice did not have normal weight gain during treatment.

CONCLUSIONS

TUDCA treatment preserved ERG b-waves and the outer nuclear layer in Bbs1(M390R/M390R) mice, and prevented obesity assessed at P120. TUDCA treatment preserved ERG b-waves and the outer nuclear layer in the rd10 mice to P30. TUDCA is a prime candidate for treatment of humans with retinal degeneration, especially those with Bardet-Biedl syndrome, whom it may help not only with the vision loss, but with the debilitating obesity as well.