New insights into the regulation of bile acids synthesis during the early stages of liver regeneration: A human and experimental study.

BACKGROUND AND AIMS: Liver regeneration is essential for the preservation of homeostasis and survival. Bile acids (BAs)-mediated signaling is necessary for liver regeneration, but BAs levels need to be carefully controlled to avoid hepatotoxicity. We studied the early response of the BAs-fibroblast growth factor 19 (FGF19) axis in healthy individuals undergoing hepatectomy for living donor liver transplant. We also evaluated BAs synthesis in mice upon partial hepatectomy (PH) and acute inflammation, focusing on the regulation of cytochrome-7A1 (CYP7A1), a key enzyme in BAs synthesis from cholesterol. METHODS: Serum was obtained from twelve human liver donors. Mice underwent 2/3-PH or sham-operation. Acute inflammation was induced with bacterial lipopolysaccharide (LPS) in mice fed control or antoxidant-supplemented diets. BAs and 7α-hydroxy-4-cholesten-3-one (C4) levels were measured by HPLC-MS/MS; serum FGF19 by ELISA. Gene expression and protein levels were analyzed by RT-qPCR and western-blot. RESULTS: Serum BAs levels increased after PH. In patients with more pronounced hypercholanemia, FGF19 concentrations transiently rose, while C4 levels (a readout of CYP7A1 activity) dropped 2 h post-resection in all cases. Serum BAs and C4 followed the same pattern in mice 1 h after PH, but C4 levels also dropped in sham-operated and LPS-treated animals, without marked changes in CYP7A1 protein levels. LPS-induced serum C4 decline was attenuated in mice fed an antioxidant-supplemented diet. CONCLUSIONS: In human liver regeneration FGF19 upregulation may constitute a protective response from BAs excess during liver regeneration. Our findings suggest the existence of post-translational mechanisms regulating CYP7A1 activity, and therefore BAs synthesis, independent from CYP7A1/Cyp7a1 gene transcription.

Selective PPARδ agonist seladelpar suppresses bile acid synthesis by reducing hepatocyte CYP7A1 via the fibroblast growth factor 21 signaling pathway.

Peroxisome proliferator-activated receptor delta (PPARδ) agonists have been shown to exert beneficial effects in liver disease and reduce total bile acid levels. The mechanism(s) whereby PPARδ agonism reduces bile acid levels are, however, unknown, and therefore the aim of the present study was to investigate the molecular pathways responsible for reducing bile acid synthesis in hepatocytes, following treatment with the selective PPARδ agonist, seladelpar. We show that administration of seladelpar to WT mice repressed the liver expression of cholesterol 7 alpha-hydroxylase (Cyp7a1), the rate-limiting enzyme for bile acid synthesis, and decreased plasma 7α-hydroxy-4-cholesten-3-one (C4), a freely diffusible metabolite downstream of Cyp7a1. In primary mouse hepatocytes, seladelpar significantly reduced the expression of Cyp7a1 independent of the nuclear bile acid receptor, Farnesoid X receptor. In addition, seladelpar upregulated fibroblast growth factor 21 (Fgf21) in mouse liver, serum, and in cultured hepatocytes. We demonstrate that recombinant Fgf21 protein activated the c-Jun N-terminal kinase (JNK) signaling pathway and repressed Cyp7a1 gene expression in primary hepatocytes. The suppressive effect of seladelpar on Cyp7a1 expression was blocked by a JNK inhibitor as well as in the absence of Fgf21, indicating that Fgf21 plays an indispensable role in PPARδ-mediated downregulation of Cyp7a1. Finally, reduction of CYP7A1 expression by seladelpar was confirmed in primary human hepatocytes. In conclusion, we show that seladelpar reduces bile acid synthesis via an FGF21-dependent mechanism that signals at least partially through JNK to repress CYP7A1.

Yogurt Enriched with Inulin Ameliorated Reproductive Functions and Regulated Gut Microbiota in Dehydroepiandrosterone-Induced Polycystic Ovary Syndrome Mice.

The effects of synbiotic yogurt supplemented with inulin on the pathological manifestations and gut microbiota-bile acid axis were investigated using a dehydroepiandrosterone (DHEA)-induced polycystic ovary syndrome (PCOS) mice model. Female C57BL/6J mice were injected subcutaneously with DHEA at a dose of 6 mg/100 g BW for 20 days to establish a PCOS mouse model. Then, the PCOS mice were treated with yogurt containing inulin (6% w/w) at 15 mL/kg BW for 24 days. Results showed that supplementation of synbiotic yogurt enriched with inulin to PCOS mice decreased the body weight gain, improved estrus cycles and ovary morphology, and reduced the levels of luteinizing hormone while increasing the levels of follicle-stimulating hormone and interleukin-22 in serum. At the genus level, synbiotic yogurt increased the relative abundance of Lactobacillus, Bifidobacterium, and Akkermansia. PICRUSt analysis indicated that KEGG pathways including bile acid biosynthesis were changed after inulin-enriched synbiotic yogurt supplementation. Synbiotic yogurt enriched with inulin also modulated the bile acid profiles. In conclusion, inulin-enriched synbiotic yogurt alleviated reproductive dysfunction and modulated gut microbiota and bile acid profiles in PCOS mice.

Low production of 12α-hydroxylated bile acids prevents hepatic steatosis in Cyp2c70-/- mice by reducing fat absorption.

Bile acids (BAs) play important roles in lipid homeostasis, and BA signaling pathways serve as therapeutic targets for nonalcoholic fatty liver disease (NAFLD). Recently, we generated cytochrome P450, family 2, subfamily C, polypeptide 70 (Cyp2c70-/-) mice with a human-like BA composition lacking mouse-/rat-specific muricholic acids to accelerate translation from mice to humans. We employed this model to assess the consequences of a human-like BA pool on diet-induced obesity and NAFLD development. Male and female Cyp2c70-/- mice and WT littermates were challenged with a 12-week high-fat Western-type diet (WTD) supplemented with 0.25% cholesterol. Cyp2c70 deficiency induced a hydrophobic BA pool with high abundances of chenodeoxycholic acid, particularly in females, because of sex-dependent suppression of sterol 12α-hydroxylase (Cyp8b1). Plasma transaminases were elevated, and hepatic fibrosis was present in Cyp2c70-/- mice, especially in females. Surprisingly, female Cyp2c70-/- mice were resistant to WTD-induced obesity and hepatic steatosis, whereas male Cyp2c70-/- mice showed similar adiposity and moderately reduced steatosis compared with WT controls. Both intestinal cholesterol and FA absorption were reduced in Cyp2c70-/- mice, the latter more strongly in females, despite unaffected biliary BA secretion rates. Intriguingly, the biliary ratio 12α-/non-12α-hydroxylated BAs significantly correlated with FA absorption and hepatic triglyceride content as well as with specific changes in gut microbiome composition. The hydrophobic human-like BA pool in Cyp2c70-/- mice prevents WTD-induced obesity in female mice and NAFLD development in both genders, primarily because of impaired intestinal fat absorption. Our data point to a key role for 12α-hydroxylated BAs in control of intestinal fat absorption and modulation of gut microbiome composition.

Bile acid synthesis, modulation, and dementia: A metabolomic, transcriptomic, and pharmacoepidemiologic study.

BACKGROUND: While Alzheimer disease (AD) and vascular dementia (VaD) may be accelerated by hypercholesterolemia, the mechanisms underlying this association are unclear. We tested whether dysregulation of cholesterol catabolism, through its conversion to primary bile acids (BAs), was associated with dementia pathogenesis. METHODS AND FINDINGS: We used a 3-step study design to examine the role of the primary BAs, cholic acid (CA), and chenodeoxycholic acid (CDCA) as well as their principal biosynthetic precursor, 7α-hydroxycholesterol (7α-OHC), in dementia. In Step 1, we tested whether serum markers of cholesterol catabolism were associated with brain amyloid accumulation, white matter lesions (WMLs), and brain atrophy. In Step 2, we tested whether exposure to bile acid sequestrants (BAS) was associated with risk of dementia. In Step 3, we examined plausible mechanisms underlying these findings by testing whether brain levels of primary BAs and gene expression of their principal receptors are altered in AD. Step 1: We assayed serum concentrations CA, CDCA, and 7α-OHC and used linear regression and mixed effects models to test their associations with brain amyloid accumulation (N = 141), WMLs, and brain atrophy (N = 134) in the Baltimore Longitudinal Study of Aging (BLSA). The BLSA is an ongoing, community-based cohort study that began in 1958. Participants in the BLSA neuroimaging sample were approximately 46% male with a mean age of 76 years; longitudinal analyses included an average of 2.5 follow-up magnetic resonance imaging (MRI) visits. We used the Alzheimer's Disease Neuroimaging Initiative (ADNI) (N = 1,666) to validate longitudinal neuroimaging results in BLSA. ADNI is an ongoing, community-based cohort study that began in 2003. Participants were approximately 55% male with a mean age of 74 years; longitudinal analyses included an average of 5.2 follow-up MRI visits. Lower serum concentrations of 7α-OHC, CA, and CDCA were associated with higher brain amyloid deposition (p = 0.041), faster WML accumulation (p = 0.050), and faster brain atrophy mainly (false discovery rate [FDR] p = <0.001-0.013) in males in BLSA. In ADNI, we found a modest sex-specific effect indicating that lower serum concentrations of CA and CDCA were associated with faster brain atrophy (FDR p = 0.049) in males.Step 2: In the Clinical Practice Research Datalink (CPRD) dataset, covering >4 million registrants from general practice clinics in the United Kingdom, we tested whether patients using BAS (BAS users; 3,208 with ≥2 prescriptions), which reduce circulating BAs and increase cholesterol catabolism, had altered dementia risk compared to those on non-statin lipid-modifying therapies (LMT users; 23,483 with ≥2 prescriptions). Patients in the study (BAS/LMT) were approximately 34%/38% male and with a mean age of 65/68 years; follow-up time was 4.7/5.7 years. We found that BAS use was not significantly associated with risk of all-cause dementia (hazard ratio (HR) = 1.03, 95% confidence interval (CI) = 0.72-1.46, p = 0.88) or its subtypes. We found a significant difference between the risk of VaD in males compared to females (p = 0.040) and a significant dose-response relationship between BAS use and risk of VaD (p-trend = 0.045) in males.Step 3: We assayed brain tissue concentrations of CA and CDCA comparing AD and control (CON) samples in the BLSA autopsy cohort (N = 29). Participants in the BLSA autopsy cohort (AD/CON) were approximately 50%/77% male with a mean age of 87/82 years. We analyzed single-cell RNA sequencing (scRNA-Seq) data to compare brain BA receptor gene expression between AD and CON samples from the Religious Orders Study and Memory and Aging Project (ROSMAP) cohort (N = 46). ROSMAP is an ongoing, community-based cohort study that began in 1994. Participants (AD/CON) were approximately 56%/36% male with a mean age of 85/85 years. In BLSA, we found that CA and CDCA were detectable in postmortem brain tissue samples and were marginally higher in AD samples compared to CON. In ROSMAP, we found sex-specific differences in altered neuronal gene expression of BA receptors in AD. Study limitations include the small sample sizes in the BLSA cohort and likely inaccuracies in the clinical diagnosis of dementia subtypes in primary care settings. CONCLUSIONS: We combined targeted metabolomics in serum and amyloid positron emission tomography (PET) and MRI of the brain with pharmacoepidemiologic analysis to implicate dysregulation of cholesterol catabolism in dementia pathogenesis. We observed that lower serum BA concentration mainly in males is associated with neuroimaging markers of dementia, and pharmacological lowering of BA levels may be associated with higher risk of VaD in males. We hypothesize that dysregulation of BA signaling pathways in the brain may represent a plausible biologic mechanism underlying these results. Together, our observations suggest a novel mechanism relating abnormalities in cholesterol catabolism to risk of dementia.

High-fiber diets attenuate emphysema development via modulation of gut microbiota and metabolism.

Dietary fiber functions as a prebiotic to determine the gut microbe composition. The gut microbiota influences the metabolic functions and immune responses in human health. The gut microbiota and metabolites produced by various dietary components not only modulate immunity but also impact various organs. Although recent findings have suggested that microbial dysbiosis is associated with several respiratory diseases, including asthma, cystic fibrosis, and allergy, the role of microbiota and metabolites produced by dietary nutrients with respect to pulmonary disease remains unclear. Therefore, we explored whether the gut microbiota and metabolites produced by dietary fiber components could influence a cigarette smoking (CS)-exposed emphysema model. In this study, it was demonstrated that a high-fiber diet including non-fermentable cellulose and fermentable pectin attenuated the pathological changes associated with emphysema progression and the inflammatory response in CS-exposed emphysema mice. Moreover, we observed that different types of dietary fiber could modulate the diversity of gut microbiota and differentially impacted anabolism including the generation of short-chain fatty acids, bile acids, and sphingolipids. Overall, the results of this study indicate that high-fiber diets play a beneficial role in the gut microbiota-metabolite modulation and substantially affect CS-exposed emphysema mice. Furthermore, this study suggests the therapeutic potential of gut microbiota and metabolites from a high-fiber diet in emphysema via local and systemic inflammation inhibition, which may be useful in the development of a new COPD treatment plan.

Exercise training and diet-induced weight loss increase markers of hepatic bile acid (BA) synthesis and reduce serum total BA concentrations in obese women.

Regular exercise has profound metabolic influence on the liver, but effects on bile acid (BA) metabolism are less well known. BAs are synthesized exclusively in the liver from cholesterol via the rate-limiting enzyme cholesterol 7 alpha-hydroxylase (CYP7A1). BAs contribute to the solubilization and absorption of lipids and serve as important signaling molecules, capable of systemic endocrine function. Circulating BAs increase with obesity and insulin resistance, but effects following exercise and diet-induced weight loss are unknown. To test if improvements in fitness and weight loss as a result of exercise training enhance BA metabolism, we measured serum concentrations of total BAs (conjugated and unconjugated primary and secondary BAs) in sedentary, obese, insulin-resistant women (N = 11) before (PRE) and after (POST) a ∼14-wk exercise and diet-induced weight loss intervention. BAs were measured in serum collected after an overnight fast and during an oral glucose tolerance test (OGTT). Serum fibroblast growth factor 19 (FGF19; a regulator of BA synthesis) and 7-alpha-hydroxy-cholesten-3-one (C4, a marker of CYP7A1 enzymatic activity) also were measured. Using linear mixed-model analyses and the change in V̇O2peak (mL/min/kg) as a covariate, we observed that exercise and weight loss intervention decreased total fasting serum BA by ∼30% (P = 0.001) and increased fasting serum C4 concentrations by 55% (P = 0.004). C4 was significantly correlated with serum total BAs only in the POST condition, whereas serum FGF19 was unchanged. These data indicate that a fitness and weight loss intervention modifies BA metabolism in obese women and suggest that improved metabolic health associates with higher postabsorptive (fasting) BA synthesis. Furthermore, pre- vs. postintervention patterns of serum C4 following an OGTT support the hypothesis that responsiveness of BA synthesis to postprandial inhibition is improved after exercise and weight loss.NEW & NOTEWORTHY Exercise and weight loss in previously sedentary, insulin-resistant women facilitates a significant improvement in insulin sensitivity and fitness that may be linked to changes in bile acid metabolism. Diet-induced weight loss plus exercise-induced increases in fitness promote greater postabsorptive bile acid synthesis while also sensitizing the bile acid metabolic system to feedback inhibition during a glucose challenge when glucose and insulin are elevated.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism.

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

Bile formation and secretion: An update.

Bile formation is a fundamental physiological process that is vital to the survival of all vertebrates. However, little was known about the mechanisms of this secretion until after World War II. Initial studies involved classic physiologic studies in animal models and humans, which progressed to include studies in isolated cells and membrane vesicles. The advent of molecular biology then led to the identification of specific transport systems that are the determinants of this secretion. Progress in this field was reviewed in the American Physiologic Society's series on "Comprehensive Physiology" in 2013. Herein, we provide an in-depth update of progress since that time.

Vertical sleeve gastrectomy confers metabolic improvements by reducing intestinal bile acids and lipid absorption in mice.

Vertical sleeve gastrectomy (VSG) is one of the most effective and durable therapies for morbid obesity and its related complications. Although bile acids (BAs) have been implicated as downstream mediators of VSG, the specific mechanisms through which BA changes contribute to the metabolic effects of VSG remain poorly understood. Here, we confirm that high fat diet-fed global farnesoid X receptor (Fxr) knockout mice are resistant to the beneficial metabolic effects of VSG. However, the beneficial effects of VSG were retained in high fat diet-fed intestine- or liver-specific Fxr knockouts, and VSG did not result in Fxr activation in the liver or intestine of control mice. Instead, VSG decreased expression of positive hepatic Fxr target genes, including the bile salt export pump (Bsep) that delivers BAs to the biliary pathway. This reduced small intestine BA levels in mice, leading to lower intestinal fat absorption. These findings were verified in sterol 27-hydroxylase (Cyp27a1) knockout mice, which exhibited low intestinal BAs and fat absorption and did not show metabolic improvements following VSG. In addition, restoring small intestinal BA levels by dietary supplementation with taurocholic acid (TCA) partially blocked the beneficial effects of VSG. Altogether, these findings suggest that reductions in intestinal BAs and lipid absorption contribute to the metabolic benefits of VSG.

Glucagon-like peptide 1 analogue prevents cholesterol gallstone formation by modulating intestinal farnesoid X receptor activity.

BACKGROUND & AIMS: Cholesterol gallstone disease (CGD) is a common gastrointestinal disease. Liraglutide, an analogue of glucagon-like peptide 1, has been approved to treat type 2 diabetes. Clinical studies have suggested a potential role of liraglutide in CGD. METHODS: Mice were subcutaneously injected with liraglutide, then fed a lithogenic diet. Bile duct cannulation was performed to collect bile output in mice. Intestinal-specific ablation or pharmacological inhibition of farnesoid X receptor (FXR) was used to study its functions in CGD. RESULTS: Liraglutide could protect mice against CGD. Liraglutide treatment increased the biliary concentration of cholesterol, phospholipids and bile acids and thereby decreased the cholesterol saturation index. The resistance to CGD conferred by liraglutide is likely a result of increased bile acid synthesis and efficient bile acid transport. The expression of a key bile acid synthetic enzyme, Cyp7a1, was significantly increased in liraglutide-treated mice. The increased expression of Cyp7a1 resulted from a relieved suppression signal of Fgf15 from the ileum. Mechanistically, liraglutide treatment altered bile acid composition and suppressed FXR activity in the ileum. Genetic ablation or pharmacological inhibition of FXR in the intestine protected mice against CGD. More importantly, intestinal FXR was required for liraglutide-mediated regulation of hepatic expression of Cyp7a1. CONCLUSION: Liraglutide improved CGD by increasing bile acid secretion and decreasing cholesterol saturation index. Liraglutide attenuates the negative feedback inhibition of bile acids through inhibiting intestinal FXR activity. Our results suggest that liraglutide may represent a novel way for treating or preventing cholesterol gallstones in individuals with high risk of CGD.

A structurally optimized FXR agonist, MET409, reduced liver fat content over 12 weeks in patients with non-alcoholic steatohepatitis.

BACKGROUND & AIMS: The benefits of farnesoid X receptor (FXR) agonists in patients with non-alcoholic steatohepatitis (NASH) have been validated, although improvements in efficacy and/or tolerability remain elusive. Herein, we aimed to assess the performance of a structurally optimized FXR agonist in patients with NASH. METHODS: In this 12-week, randomized, placebo-controlled study, we evaluated MET409 - a non-bile acid agonist with a unique chemical scaffold - in patients with NASH. Patients were randomized to receive either 80 mg (n = 20) or 50 mg (n = 19) of MET409, or placebo (n = 19). RESULTS: At Week 12, MET409 lowered liver fat content (LFC), with mean relative reductions of 55% (80 mg) and 38% (50 mg) vs. 6% in placebo (p <0.001). MET409 achieved ≥30% relative LFC reduction in 93% (80 mg) and 75% (50 mg) of patients vs. 11% in placebo (p <0.001) and normalized LFC (≤5%) in 29% (80 mg) and 31% (50 mg) of patients vs. 0% in placebo (p <0.05). An increase in alanine aminotransferase (ALT) was observed with MET409, confounding Week 12 changes from baseline (-25% for 80 mg, 28% for 50 mg). Nonetheless, MET409 achieved ≥30% relative ALT reduction in 50% (80 mg) and 31% (50 mg) of patients vs. 17% in placebo. MET409 was associated with on-target high-density lipoprotein cholesterol decreases (mean changes of -23.4% for 80 mg and -20.3% for 50 mg vs. 2.6% in placebo) and low-density lipoprotein cholesterol (LDL-C) increases (mean changes of 23.7% for 80 mg and 6.8% for 50 mg vs. -1.5% in placebo). Pruritus (mild-moderate) occurred in 16% (50 mg) and 40% (80 mg) of MET409-treated patients. CONCLUSION: MET409 lowered LFC over 12 weeks in patients with NASH and delivered a differentiated pruritus and LDL-C profile at 50 mg, providing the first clinical evidence that the risk-benefit profile of FXR agonists can be enhanced through structural optimization. LAY SUMMARY: Activation of the farnesoid X receptor (FXR) is a clinically validated approach for treating non-alcoholic steatohepatitis (NASH), although side effects such as itching or increases in low-density lipoprotein cholesterol are frequently dose-limiting. MET409, an FXR agonist with a unique chemical structure, led to significant liver fat reduction and delivered a favorable side effect profile after 12 weeks of treatment in patients with NASH. These results provide the first clinical evidence that the risk-benefit profile of FXR agonists can be enhanced.

Bile Acid Synthesis Disorders in Japan: Long-Term Outcome and Chenodeoxycholic Acid Treatment.

BACKGROUND: We encountered 7 Japanese patients with bile acid synthesis disorders (BASD) including 3ß-hydroxy-Δ5-C27-steroid dehydrogenase/isomerase (3ß-HSD) deficiency (n = 3), Δ4-3-oxosteroid 5ß-reductase (5ß-reductase) deficiency (n = 3), and oxysterol 7α-hydroxylase deficiency (n = 1) over 21 years between 1996 and 2017. AIM: We aimed to clarify long-term outcome in the 7 patients with BASD as well as long-term efficacy of chenodeoxycholic acid (CDCA) treatment in the 5 patients with 3ß-HSD deficiency or 5ß-reductase deficiency. METHODS: Diagnoses were made from bile acid and genetic analyses. Bile acid analysis in serum and urine was performed using gas chromatography-mass spectrometry. Clinical and laboratory findings and bile acid profiles at diagnosis and most recent visit were retrospectively obtained from medical records. Long-term outcome included follow-up duration, treatments, growth, education/employment, complications of treatment, and other problems. RESULTS: Medians with ranges of current patient ages and duration of CDCA treatment are 10 years (8 to 43) and 10 years (8 to 21), respectively. All 7 patients, who had homozygous or compound heterozygous mutations in the HSD3B7, SRD5B1, or CYP7B1 gene, are currently in good health without liver dysfunction. In the 5 patients with CDCA treatment, hepatic function gradually improved following initiation. No adverse effects were noted. CONCLUSIONS: We concluded that CDCA treatment is effective in 3ß-HSD deficiency and 5ß-reductase deficiency, as cholic acid has been in other countries. BASD carry a good prognosis following early diagnosis and initiation of long-term CDCA treatment.

STARD1 promotes NASH-driven HCC by sustaining the generation of bile acids through the alternative mitochondrial pathway.

BACKGROUND & AIMS: Besides their physiological role in bile formation and fat digestion, bile acids (BAs) synthesised from cholesterol in hepatocytes act as signalling molecules that modulate hepatocellular carcinoma (HCC). Trafficking of cholesterol to mitochondria through steroidogenic acute regulatory protein 1 (STARD1) is the rate-limiting step in the alternative pathway of BA generation, the physiological relevance of which is not well understood. Moreover, the specific contribution of the STARD1-dependent BA synthesis pathway to HCC has not been previously explored. METHODS: STARD1 expression was analyzed in a cohort of human non-alcoholic steatohepatitis (NASH)-derived HCC specimens. Experimental NASH-driven HCC models included MUP-uPA mice fed a high-fat high-cholesterol (HFHC) diet and diethylnitrosamine (DEN) treatment in wild-type (WT) mice fed a HFHC diet. Molecular species of BAs and oxysterols were analyzed by mass spectrometry. Effects of NASH-derived BA profiles were investigated in tumour-initiated stem-like cells (TICs) and primary mouse hepatocytes (PMHs). RESULTS: Patients with NASH-associated HCC exhibited increased hepatic expression of STARD1 and an enhanced BA pool. Using NASH-driven HCC models, STARD1 overexpression in WT mice increased liver tumour multiplicity, whereas hepatocyte-specific STARD1 deletion (Stard1ΔHep) in WT or MUP-uPA mice reduced tumour burden. These findings mirrored the levels of unconjugated primary BAs, ß-muricholic acid and cholic acid, and their tauroconjugates in STARD1-overexpressing and Stard1ΔHep mice. Incubation of TICs or PMHs with a mix of BAs mimicking this profile stimulated expression of genes involved in pluripotency, stemness and inflammation. CONCLUSIONS: The study reveals a previously unrecognised role of STARD1 in HCC pathogenesis, wherein it promotes the synthesis of primary BAs through the mitochondrial pathway, the products of which act in TICs to stimulate self-renewal, stemness and inflammation. LAY SUMMARY: Effective therapy for hepatocellular carcinoma (HCC) is limited because of our incomplete understanding of its pathogenesis. The contribution of the alternative pathway of bile acid (BA) synthesis to HCC development is unknown. We uncover a key role for steroidogenic acute regulatory protein 1 (STARD1) in non-alcoholic steatohepatitis-driven HCC, wherein it stimulates the generation of BAs in the mitochondrial acidic pathway, the products of which stimulate hepatocyte pluripotency and self-renewal, as well as inflammation.

Soybean-Derived Peptides Attenuate Hyperlipidemia by Regulating Trans-Intestinal Cholesterol Excretion and Bile Acid Synthesis.

Increased triglyceride, cholesterol, and low-density lipoprotein (LDL) levels cause hyperlipidemia. Despite the availability of statin-based drugs to reduce LDL levels, additional effective treatments for reducing blood lipid concentrations are required. Herein, soybean hydrolysate prepared via peptic and tryptic hydrolysis promoted trans-intestinal cholesterol excretion (TICE) by increasing ATP-binding cassette subfamily G member 5 (ABCG5) and ABCG8 expression. The peptide sequence capable of promoting TICE was determined via HPLC and LC-MS/MS. Based on this, pure artificial peptides were synthesized, and the efficacy of the selected peptides was verified using cellular and hyperlipidemic mouse models. Soybean hydrolysates, including two bioactive peptides (ALEPDHRVESEGGL and SLVNNDDRDSYRLQSGDAL), promoted TICE via the expression of ABCG5 and ABCG8 in enterocytes. They downregulated expression of hepatic cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and CYP8B1 via expression of fibroblast growth factor 19 (FGF19) in a liver X receptor α (LXRa)-dependent pathway. Administration of bioactive peptides to hyperlipidemic mouse models by oral gavage reduced cholesterol levels in serum via upregulation of ABCG5 and ABCG8 expression in the proximal intestine and through fecal cholesterol excretion, upregulated FGF 15/19 expression, and suppressed hepatic bile acid synthesis. Oral administration of soybean-derived bioactive peptides elicited hypolipidemic effects by increasing TICE and decreasing hepatic cholesterol synthesis.

Dietary supplementation with aromatic amino acids decreased triglycerides and alleviated hepatic steatosis by stimulating bile acid synthesis in mice.

Emerging evidence shows that amino acids can modulate lipid metabolism. Aromatic amino acids (AAAs) serve as important precursors of several neurotransmitters and metabolic regulators that play a vital role in regulating nutrient metabolism. But whether AAAs have a lipid-lowering function remains unknown. Here mice were fed amino acid-defined diets containing AAAs at 1.82% and 3.64% for 3 weeks. We demonstrated that double AAA intake significantly decreased the serum and hepatic triglycerides and serum low-density lipoprotein cholesterol, but increased the high-density lipoprotein cholesterol as well as insulin tolerance. Combined metabolomic and transcriptomic analysis showed that the hepatic acidic pathway of bile acid synthesis was responsible for the improvement in lipid metabolism by AAA treatment. This study suggests that AAAs have the potential to ameliorate steatosis and provides a new alternative to improve lipid metabolism.

Bile acid biosynthesis in Smith-Lemli-Opitz syndrome bypassing cholesterol: Potential importance of pathway intermediates.

Bile acids are the end products of cholesterol metabolism secreted into bile. They are essential for the absorption of lipids and lipid soluble compounds from the intestine. Here we have identified a series of unusual Δ5-unsaturated bile acids in plasma and urine of patients with Smith-Lemli-Opitz syndrome (SLOS), a defect in cholesterol biosynthesis resulting in elevated levels of 7-dehydrocholesterol (7-DHC), an immediate precursor of cholesterol. Using liquid chromatography - mass spectrometry (LC-MS) we have uncovered a pathway of bile acid biosynthesis in SLOS avoiding cholesterol starting with 7-DHC and proceeding through 7-oxo and 7ß-hydroxy intermediates. This pathway also occurs to a minor extent in healthy humans, but elevated levels of pathway intermediates could be responsible for some of the features SLOS. The pathway is also active in SLOS affected pregnancies as revealed by analysis of amniotic fluid. Importantly, intermediates in the pathway, 25-hydroxy-7-oxocholesterol, (25R)26-hydroxy-7-oxocholesterol, 3ß-hydroxy-7-oxocholest-5-en-(25R)26-oic acid and the analogous 7ß-hydroxysterols are modulators of the activity of Smoothened (Smo), an oncoprotein that mediates Hedgehog (Hh) signalling across membranes during embryogenesis and in the regeneration of postembryonic tissue. Computational docking of the 7-oxo and 7ß-hydroxy compounds to the extracellular cysteine rich domain of Smo reveals that they bind in the same groove as both 20S-hydroxycholesterol and cholesterol, known activators of the Hh pathway.

Hypothyroidism Increases Cholesterol Gallstone Prevalence in Mice by Elevated Hydrophobicity of Primary Bile Acids.

Background: Thyroid hormone (TH) deficiency has been associated with increased cholesterol gallstone prevalence. Hypothyroidism impacts hepatic lipid homeostasis, biliary secretion, gallbladder motility, and gallstone (LITH) gene expression, all potential factors contributing to cholesterol gallstone disease (CGD). However, how TH deficiency may lead to gallstone formation is still poorly understood. Therefore, we performed molecular studies in a CGD mouse model under lithogenic conditions and modulation of TH status. Methods: Male, three-month-old C57BL/6 mice were randomly divided into a control (euthyroid) group, a hypothyroid (hypo) group, a gallstone (litho) group, and a gallstone+hypothyroid (litho+hypo) group and were treated for 2, 4, and 6 weeks (n = 8/treatment period). Gallstone prevalence, biliary composition and cholesterol crystals, hepatic expression of genes participating in cholesterol, bile acid (BA), and phosphatidylcholine synthesis (Hmgcr, Cyp7a1, Pcyt1a), and canalicular transport (Abcg5, Bsep, Abcb4) were investigated. Results: Increased cholesterol gallstone prevalence was observed in hypothyroid mice under lithogenic diet after 4 and 6 weeks of treatment (4 weeks: 25% vs. 0%; 6 weeks: 75% vs. 37.5%). Interestingly, neither the composition of the three main biliary components, cholesterol, BAs, and phosphatidylcholine, nor the hepatic expression of genes involved in synthesis and transport could explain the differences in cholesterol gallstone formation in the mice. However, TH deficiency resulted in significantly increased hydrophobicity of primary BAs in bile. Furthermore, downregulation of hepatic sulfonation enzymes Papss2 and Sult2a8 as well as diminished biliary BA sulfate concentrations in mice were observed under hypothyroid conditions all contributing to a lithogenic biliary milieu as evidenced by microscopic cholesterol crystals and macroscopic gallstone formation. Conclusions: We describe a novel pathogenic link between TH deficiency and CGD and suggest that the increased hydrophobic character of biliary BAs due to the diminished expression of hepatic detoxification enzymes promotes cholesterol crystal precipitation and enhances cholesterol gallstone formation in the bile of hypothyroid mice.

Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging.

Over the past two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

Augmenter of Liver Regeneration (ALR) regulates bile acid synthesis and attenuates bile acid-induced apoptosis via glycogen synthase kinase-3ß (GSK-3ß) inhibition.

Bile acid synthesis is restricted to hepatocytes and is rate-limited by CYP7A1 (cholesterol 7α hydroxylase). CYP7A1 expression undergoes tight regulation and is repressed after partial hepatectomy to prevent the accumulation of toxic bile acids. Augmenter of Liver Regeneration (ALR) is a hepatotrophic factor shown to support liver regeneration by augmenting cell proliferation and reducing apoptosis. Nevertheless, less is known about ALR's role in protecting hepatocytes from bile acid accumulation and bile acid-induced apoptosis. Therefore, HepG2 and Huh-7 cells were incubated with recombinant human ALR (rALR) and the expression of CYP7A1, bile acid-induced apoptosis as well as potential molecular mechanisms were analyzed. We found that rALR reduces CYP7A1 expression by increasing nuclear NFκB levels. Moreover, rALR reduced glycochenodeoxycholate (GCDC)-induced-apoptosis by decreased expression of pro-apoptotic Bax and enhanced expression of anti-apoptotic Mcl-1, which is regulated by phosphatidylinositol-3-kinase (PI3K)/Akt activation and glycogen synthase kinase-3ß (GSK3ß) phosphorylation. Inhibitors for PI3K/Akt (GSK690693) and GSK3ß (SB415286) confirmed the specificity of rALR treatment for this pathway. In addition, rALR reduces pro-death signaling by decreasing GCDC-induced JNK phosphorylation. Taken all together, rALR might contribute to protecting hepatocytes from toxic concentrations of bile acids by down-regulating their denovo synthesis, attenuating apoptosis by activation of PI3K/Akt - GSK3ß pathway and inhibition of JNK signaling. Thereby this suggests a new role of ALR in augmenting the process of liver regeneration.