The bile acid synthetic gene 3beta-hydroxy-Delta(5)-C(27)-steroid oxidoreductase is mutated in progressive intrahepatic cholestasis

Glucocorticoid activation by HSD11B1 limits T cell-driven interferon signaling and response to PD-1 blockade in melanoma

BACKGROUND

Immune responses against tumors are subject to negative feedback regulation. Immune checkpoint inhibitors (ICIs) blocking Programmed cell death protein 1 (PD-1), a receptor expressed on T cells, or its ligand PD-L1 have significantly improved the treatment of cancer, in particular malignant melanoma. Nevertheless, responses and durability are variables, suggesting that additional critical negative feedback mechanisms exist and need to be targeted to improve therapeutic efficacy.

METHODS

We used different syngeneic melanoma mouse models and performed PD-1 blockade to identify novel mechanisms of negative immune regulation. Genetic gain-of-function and loss-of-function approaches as well as small molecule inhibitor applications were used for target validation in our melanoma models. We analyzed mouse melanoma tissues from treated and untreated mice by RNA-seq, immunofluorescence and flow cytometry to detect changes in pathway activities and immune cell composition of the tumor microenvironment. We analyzed tissue sections of patients with melanoma by immunohistochemistry as well as publicly available single-cell RNA-seq data and correlated target expression with clinical responses to ICIs.

RESULTS

Here, we identified 11-beta-hydroxysteroid dehydrogenase-1 (HSD11B1), an enzyme that converts inert glucocorticoids into active forms in tissues, as negative feedback mechanism in response to T cell immunotherapies. Glucocorticoids are potent suppressors of immune responses. HSD11B1 was expressed in different cellular compartments of melanomas, most notably myeloid cells but also T cells and melanoma cells. Enforced expression of HSD11B1 in mouse melanomas limited the efficacy of PD-1 blockade, whereas small molecule HSD11B1 inhibitors improved responses in a CD8+ T cell-dependent manner. Mechanistically, HSD11B1 inhibition in combination with PD-1 blockade augmented the production of interferon-γ by T cells. Interferon pathway activation correlated with sensitivity to PD-1 blockade linked to anti-proliferative effects on melanoma cells. Furthermore, high levels of HSD11B1, predominantly expressed by tumor-associated macrophages, were associated with poor responses to ICI therapy in two independent cohorts of patients with advanced melanomas analyzed by different methods (scRNA-seq, immunohistochemistry).

CONCLUSION

As HSD11B1 inhibitors are in the focus of drug development for metabolic diseases, our data suggest a drug repurposing strategy combining HSD11B1 inhibitors with ICIs to improve melanoma immunotherapy. Furthermore, our work also delineated potential caveats emphasizing the need for careful patient stratification.

Novel mutation in the HSD3B7 gene causes bile acid synthetic disorder and presents as recurrent liver failure in early childhood

Bile acid synthetic disorders are rare inborn errors of metabolism, and presentations include neonatal cholestasis, neurological disease or deficiency of fat-soluble vitamins. Affected patients fail to produce standard bile acids but accumulate unusual bile acids and intermediates, resulting in liver failure and complications. Most of them improve with bile acid supplementation, but delaying initiating treatment is detrimental to the outcome.A young child presented to us with recurrent episodes of acute liver failure. In the first episode, both coagulopathy and encephalopathy improved on supportive treatment, but the aetiological evaluation was inconclusive. During the second presentation, whole-exome sequencing was sent, identifying a compound heterozygous novel mutation in the 3-β-hydroxysteroid dehydrogenase type 7 gene leading to bile acid synthetic defect.

Cholesterol metabolism: from lipidomics to immunology

Oxysterols, the oxidized forms of cholesterol or of its precursors, are formed in the first steps of cholesterol metabolism. Oxysterols have interested chemists, biologists, and physicians for many decades, but their exact biological relevance in vivo, other than as intermediates in bile acid biosynthesis, has long been debated. However, in the first quarter of this century, a role for side-chain oxysterols and their C-7 oxidized metabolites has been convincingly established in the immune system. 25-Hydroxycholesterol has been shown to be synthesized by macrophages in response to the activation of Toll-like receptors and to offer protection against microbial pathogens, whereas 7α,25-dihydroxycholesterol has been shown to act as a chemoattractant to lymphocytes expressing the G protein-coupled receptor Epstein-Barr virus-induced gene 2 and to be important in coordinating the action of B cells, T cells, and dendritic cells in secondary lymphoid tissue. There is a growing body of evidence that not only these two oxysterols but also many of their isomers are of importance to the proper function of the immune system. Here, we review recent findings related to the roles of oxysterols in immunology.

Genetic spectrum and clinical characteristics of 3β-hydroxy-Δ5-C27-steroid oxidoreductase (HSD3B7) deficiency in China

BACKGROUND

Biallelic variants in HSD3B7 cause 3β-hydroxy-Δ5-C27-steroid oxidoreductase (HSD3B7) deficiency, a life-threatening but treatable liver disease. The goal of this study was to obtain detailed information on the correlation between the genotype and phenotype of HSD3B7 deficiency and to report on responses to primary bile acid therapy.

METHODS

The medical records of a cohort of 39 unrelated patients with genetically and biochemically confirmed HSD3B7 deficiency were examined to determine whether there exist genotype-phenotype relationships in this bile acid synthesis disorder.

RESULTS

In all, 34 of the 44 variants identified in HSD3B7 were novel. A total of 32 patients presented early with neonatal cholestasis, and 7 presented after 1-year of age with liver failure (n = 1), liver cirrhosis (n = 3), cholestasis (n = 1), renal cysts and abnormal liver biochemistries (n = 1), and coagulopathy from vitamin K1 deficiency and abnormal liver biochemistries (n = 1). Renal lesions, including renal cysts, renal stones, calcium deposition and renal enlargement were observed in 10 of 35 patients. Thirty-three patients were treated with oral chenodeoxycholic acid (CDCA) resulting in normalization of liver biochemistries in 24, while 2 showed a significant clinical improvement, and 7 underwent liver transplantation or died. Remarkably, renal lesions in 6 patients resolved after CDCA treatment, or liver transplantation. There were no significant correlations between genotype and clinical outcomes.

CONCLUSIONS

In what is the largest cohort of patients with HSD3B7 deficiency thus far studied, renal lesions were a notable clinical feature of HSD3B7 deficiency and these were resolved with suppression of atypical bile acids by oral CDCA administration.

Osteoblasts Generate Testosterone From DHEA and Activate Androgen Signaling in Prostate Cancer Cells

Bone metastasis is a complication of prostate cancer in up to 90% of men afflicted with advanced disease. Therapies that reduce androgen exposure remain at the forefront of treatment. However, most prostate cancers transition to a state whereby reducing testicular androgen action becomes ineffective. A common mechanism of this transition is intratumoral production of testosterone (T) using the adrenal androgen precursor dehydroepiandrosterone (DHEA) through enzymatic conversion by 3β- and 17β-hydroxysteroid dehydrogenases (3βHSD and 17βHSD). Given the ability of prostate cancer to form blastic metastases in bone, we hypothesized that osteoblasts might be a source of androgen synthesis. RNA expression analyses of murine osteoblasts and human bone confirmed that at least one 3βHSD and 17βHSD enzyme isoform was expressed, suggesting that osteoblasts are capable of generating androgens from adrenal DHEA. Murine osteoblasts were treated with 100 nM and 1 μM DHEA or vehicle control. Conditioned media from these osteoblasts were assayed for intermediate and active androgens by liquid chromatography-tandem mass spectrometry. As DHEA was consumed, the androgen intermediates androstenediol and androstenedione were generated and subsequently converted to T. Conditioned media of DHEA-treated osteoblasts increased androgen receptor (AR) signaling, prostate-specific antigen (PSA) production, and cell numbers of the androgen-sensitive prostate cancer cell lines C4-2B and LNCaP. DHEA did not induce AR signaling in osteoblasts despite AR expression in this cell type. We describe an unreported function of osteoblasts as a source of T that is especially relevant during androgen-responsive metastatic prostate cancer invasion into bone. © 2021 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Microbial Hydroxysteroid Dehydrogenases: From Alpha to Omega

Bile acids (BAs) and glucocorticoids are steroid hormones derived from cholesterol that are important signaling molecules in humans and other vertebrates. Hydroxysteroid dehydrogenases (HSDHs) are encoded both by the host and by their resident gut microbiota, and they reversibly convert steroid hydroxyl groups to keto groups. Pairs of HSDHs can reversibly epimerize steroids from α-hydroxy conformations to β-hydroxy, or β-hydroxy to ω-hydroxy in the case of ω-muricholic acid. These reactions often result in products with drastically different physicochemical properties than their precursors, which can result in steroids being activators or inhibitors of host receptors, can affect solubility in fecal water, and can modulate toxicity. Microbial HSDHs modulate sterols associated with diseases such as colorectal cancer, liver cancer, prostate cancer, and polycystic ovary syndrome. Although the role of microbial HSDHs is not yet fully elucidated, they may have therapeutic potential as steroid pool modulators or druggable targets in the future. In this review, we explore metabolism of BAs and glucocorticoids with a focus on biotransformation by microbial HSDHs.

3β-Isoobeticholic acid efficiently activates the farnesoid X receptor (FXR) due to its epimerization to 3α-epimer by hepatic metabolism

Bile acids (BAs) are important signaling molecules acting via the farnesoid X nuclear receptor (FXR) and the membrane G protein-coupled bile acid receptor 1 (GPBAR1). Besides deconjugation of BAs, the oxidoreductive enzymes of colonic bacteria and hepatocytes enable the conversion of BAs into their epimers or dehydrogenated forms. Obeticholic acid (OCA) is the first-in-class BA-derived FXR agonist approved for the treatment of primary biliary cholangitis. Herein, a library of OCA derivatives, including 7-keto, 6-ethylidene derivatives and 3β-epimers, was synthetized and investigated in terms of interactions with FXR and GPBAR1 in transaction assays and evaluated for FXR target genes expression in human hepatocytes and C57BL/6 mice. The derivatives were further subjected to cell-free analysis employing in silico molecular docking and a TR-FRET assay. The conversion of the 3βhydroxy epimer and its pharmacokinetics in mice were studied using LC-MS. We found that only the 3β-hydroxy epimer of OCA (3β-isoOCA) possesses significant activity to FXR in hepatic cells and mice. However, in a cell-free assay, 3β-isoOCA had about 9-times lower affinity to FXR than did OCA. We observed that 3β-isoOCA readily epimerizes to OCA in hepatocytes and murine liver. This conversion was significantly inhibited by the hydroxy-Δ⁵-steroid dehydrogenase inhibitor trilostane. In addition, we found that 3,7-dehydroobeticholic acid is a potent GPBAR1 agonist. We conclude that 3β-isoOCA significantly activates FXR due to its epimerization to the more active OCA by hepatic metabolism. Other modifications as well as epimerization on the C3/C7 positions and the introduction of 6-ethylidene in the CDCA scaffold abrogate FXR agonism and alleviate GPBAR1 activation.

Transcriptomic profiling of PBDE-exposed HepaRG cells unveils critical lncRNA- PCG pairs involved in intermediary metabolism

Polybrominated diphenyl ethers (PBDEs) were formally used as flame-retardants and are chemically stable, lipophlic persistent organic pollutants which are known to bioaccumulate in humans. Although its toxicities are well characterized, little is known about the changes in transcriptional regulation caused by PBDE exposure. Long non-coding RNAs (lncRNAs) are increasingly recognized as key regulators of transcriptional and translational processes. It is hypothesized that lncRNAs can regulate nearby protein-coding genes (PCGs) and changes in the transcription of lncRNAs may act in cis to perturb gene expression of its neighboring PCGs. The goals of this study were to 1) characterize PCGs and lncRNAs that are differentially regulated from exposure to PBDEs; 2) identify PCG-lncRNA pairs through genome annotation and predictive binding tools; and 3) determine enriched canonical pathways caused by differentially expressed lncRNA-PCGs pairs. HepaRG cells, which are human-derived hepatic cells that accurately represent gene expression profiles of human liver tissue, were exposed to BDE-47 and BDE-99 at a dose of 25 μM for 24 hours. Differentially expressed lncRNA-PCG pairs were identified through DESeq2 and HOMER; significant canonical pathways were determined through Ingenuity Pathway Analysis (IPA). LncTar was used to predict the binding of 19 lncRNA-PCG pairs with known roles in drug-processing pathways. Genome annotation revealed that the majority of the differentially expressed lncRNAs map to PCG introns. PBDEs regulated overlapping pathways with PXR and CAR such as protein ubiqutination pathway and peroxisome proliferator-activated receptor alpha-retinoid X receptor alpha (PPARα-RXRα) activation but also regulate distinctive pathways involved in intermediary metabolism. PBDEs uniquely down-regulated GDP-L-fucose biosynthesis, suggesting its role in modifying important pathways involved in intermediary metabolism such as carbohydrate and lipid metabolism. In conclusion, we provide strong evidence that PBDEs regulate both PCGs and lncRNAs in a PXR/CAR ligand-dependent and independent manner.

The Biosynthesis of Enzymatically Oxidized Lipids

Enzymatically oxidized lipids are a specific group of biomolecules that function as key signaling mediators and hormones, regulating various cellular and physiological processes from metabolism and cell death to inflammation and the immune response. They are broadly categorized as either polyunsaturated fatty acid (PUFA) containing (free acid oxygenated PUFA "oxylipins", endocannabinoids, oxidized phospholipids) or cholesterol derivatives (oxysterols, steroid hormones, and bile acids). Their biosynthesis is accomplished by families of enzymes that include lipoxygenases (LOX), cyclooxygenases (COX), cytochrome P450s (CYP), and aldo-keto reductases (AKR). In contrast, non-enzymatically oxidized lipids are produced by uncontrolled oxidation and are broadly considered to be harmful. Here, we provide an overview of the biochemistry and enzymology of LOXs, COXs, CYPs, and AKRs in humans. Next, we present biosynthetic pathways for oxylipins, oxidized phospholipids, oxysterols, bile acids and steroid hormones. Last, we address gaps in knowledge and suggest directions for future work.

The Adrenal Lipid Droplet is a New Site for Steroid Hormone Metabolism

Steroid hormones play essential roles for living organisms. It has been long and well established that the endoplasmic reticulum (ER) and mitochondria are essential sites for steroid hormone biosynthesis because several steroidogenic enzymes are located in these organelles. The adrenal gland lipid droplet (LD) proteomes from human, macaque monkey, and rodent are analyzed, revealing that steroidogenic enzymes are also present in abundance on LDs. The enzymes found include 3β-hydroxysteroid dehydrogenase (HSD3B) and estradiol 17β-dehydrogenase 11 (HSD17B11). Analyses by Western blot and subcellular localization consistently demonstrate that HSD3B2 is localized on LDs. Furthermore, in vitro experiments confirm that the isolated LDs from HeLa cell stably expressing HSD3B2 or from rat adrenal glands have the capacity to convert pregnenolone to progesterone. Collectively, these data suggest that LDs may be important sites of steroid hormone metabolism. These findings may bring novel insights into the biosynthesis and metabolism of steroid hormones and the development of treatments for adrenal disorders.

Lucky, times ten: A career in Texas science

On January 21, 2017, I received an E-mail from Herb Tabor that I had been simultaneously hoping for and dreading for several years: an invitation to write a "Reflections" article for the Journal of Biological Chemistry On the one hand, I was honored to receive an invitation from Herb, a man I have admired for over 40 years, known for 24 years, and worked with as a member of the Editorial Board and Associate Editor of the Journal of Biological Chemistry for 17 years. On the other hand, the invitation marked the waning of my career as an academic scientist. With these conflicting emotions, I wrote this article with the goals of recording my career history and recognizing the many mentors, trainees, and colleagues who have contributed to it and, perhaps with pretension, with the desire that students who are beginning a career in research will find inspiration in the path I have taken and appreciate the importance of luck.

Cholic acid for primary bile acid synthesis defects: a life-saving therapy allowing a favorable outcome in adulthood

Background

Oral cholic acid (CA) replacement has been shown to be an effective therapy in children with primary bile acid synthesis defects, which are rare and severe genetic liver diseases. To date there has been no report of the effects of this therapy in children reaching adulthood. The aim of the study was to evaluate the long-term effectiveness and safety of CA therapy.

Methods

Fifteen patients with either 3β-hydroxy-Δ⁵-C₂₇-steroid oxidoreductase (3β-HSD) (n = 13) or Δ⁴–3-oxosteroid 5β-reductase (Δ⁴–3-oxo-R) (n = 2) deficiency confirmed by mass spectrometry and gene sequencing received oral CA and were followed prospectively.

Results

The median age at last follow-up and the median time of follow-up with treatment were 24.3 years (range: 15.3–37.2) and 21.4 years (range: 14.6–24.1), respectively. At last evaluation, physical examination findings and blood laboratory test results were normal in all patients. Liver sonograms were normal in most patients. Mean daily CA dose was 6.9 mg/kg of body weight. Mass spectrometry analysis of urine showed that excretion of the atypical metabolites remained low or traces in amount with CA therapy. Liver fibrosis scored in liver biopsies or assessed by elastography in 14 patients, after 10 to 24 years with CA therapy, showed a marked improvement with disappearance of cirrhosis (median score < F1; range: F0-F2). CA was well tolerated in all patients, including five women having 10 uneventful pregnancies during treatment.

Conclusions

Oral CA therapy is a safe and effective long-term treatment of 3β-HSD and Δ⁴–3-oxo-R deficiencies and allows affected children to reach adulthood in good health condition without the need for a liver transplantation.

Atypical clinical presentation and successful treatment with oral cholic acid of a child with defective bile acid synthesis due to a novel mutation in the HSD3B7 gene

We report definitive diagnosis and effective treatment with oral cholic acid in one Italian male child affected by 3β-hydroxy-Δ⁵-C²⁷-steroid dehydrogenase (3β-HSD) deficiency. He presented with failure to thrive, hepatomegaly and multiple cystic images in kidneys; no biochemical evidence of cholestasis. Large amounts of bile acid metabolites was detected in urine by fast atom bombardment ionization mass spectrometry (FAB-MS). HSDH3B7 gene analysis identified one mutation in intron 4, at nucleotide 432, G>A substitution that has never been reported before.The replacement therapy with oral cholic acid started early after the diagnosis and is still ongoing. Three years later hepatomegaly is no longer evident, liver function is normal and the child is growing regularly. In our experience, clinical features of 3β-HSD deficiency can be very poor and even cholestasis can lack at diagnosis. Early replacement therapy with cholic acid is safe and leads to clinical and biochemical control of the disease.

Liver and the defects of cholesterol and bile acids biosynthesis: Rare disorders many diagnostic pitfalls

In recent decades, biotechnology produced a growth of knowledge on the causes and mechanisms of metabolic diseases that have formed the basis for their study, diagnosis and treatment. Unfortunately, it is well known that the clinical features of metabolic diseases can manifest themselves with very different characteristics and escape early detection. Also, it is well known that the prognosis of many metabolic diseases is excellent if diagnosed and treated early. In this editorial we briefly summarized two groups of inherited metabolic diseases, the defects of cholesterol biosynthesis and those of bile acids. Both groups show variable clinical manifestations but some clinical signs and symptoms are common in both the defects of cholesterol and bile acids. The differential diagnosis can be made analyzing sterol profiles in blood and/or bile acids in blood and urine by chromatographic techniques (GC-MS and LC-MS/MS). Several defects of both biosynthetic pathways are treatable so early diagnosis is crucial. Unfortunately their diagnosis is made too late, due either to the clinical heterogeneity of the syndromes (severe, mild and very mild) that to the scarcity of scientific dissemination of these rare diseases. Therefore, the delay in diagnosis leads the patient to the medical observation when the disease has produced irreversible damages to the body. Here, we highlighted simple clinical and laboratory descriptions that can potentially make you to suspect a defect in cholesterol biosynthesis and/or bile acids, as well, we suggest appropriate request of the laboratory tests that along with common clinical features can help to diagnose these defects.

Attempt to Determine the Prevalence of Two Inborn Errors of Primary Bile Acid Synthesis: Results of a European Survey

OBJECTIVE

Inborn errors of primary bile acid (BA) synthesis are genetic cholestatic disorders leading to accumulation of atypical BA with deficiency of normal BA. Unless treated with primary BA, chronic liver disease usually progresses to cirrhosis and liver failure before adulthood. We sought to determine the prevalence of 2 common disorders, 3β-hydroxy-Δ-C27-steroid dehydrogenase (3β-HSD) and Δ-3-oxosteroid-5β-reductase (Δ-3-oxoR) deficiencies and to describe current diagnostic and treatment strategies among different European paediatric hepatology centres.

METHODS

A total of 52 clinical paediatric centres were approached and 39 centres in 21 countries agreed to participate in the Web-based survey. The survey comprised questions regarding general information, number of cases, diagnostic, and therapeutic management.

RESULTS

Seventeen centres located in 11 countries reported patients with inborn errors in primary BA synthesis, 22 centres never had cases diagnosed. In total, we could identify 63 patients; 55 with 3β-HSD and 8 with Δ-3-oxoR deficiency in 21 countries. The minimum estimated combined prevalence of these diseases was 1.13 cases per 10 million (0.99 and 0.14 for 3β-HSD and Δ-3-oxoR deficiencies, respectively). The surveyed colleagues indicated their main challenges to be the rarity of diseases and the lack of convenient laboratory facilities nearby.

CONCLUSION

We have identified the largest cohort of patients with 3β-HSD or Δ-3-oxoR deficiency described so far. These diseases are likely underdiagnosed mainly due to unawareness of their existence and the lack of laboratory facilities.

Bile acid synthesis precursors in subjects with genetic hypercholesterolemia negative for LDLR/APOB/PCSK9/APOE mutations. Association with lipids and carotid atherosclerosis

Some oxysterols are precursors of bile acid synthesis and play an important role in cholesterol homeostasis. However, if they are involved in the pathogeny of genetic hypercholesterolemia has not been previously explored. We have studied non-cholesterol sterol markers of cholesterol synthesis (lanosterol and desmosterol) and oxysterols (7α-hydroxy-4-cholesten-3-one, 24S-hydroxycholesterol and 27-hydroxycholesterol) in 200 affected subjects with primary hypercholesterolemia of genetic origin, negative for mutations in LDLR, APOB, PCSK9 and APOE genes (non-FH GH) and 100 normolipemic controls. All studied oxysterols and cholesterol synthesis markers were significantly higher in affected subjects than controls (P<0.001). Ratios of oxysterols to total cholesterol were higher in non-FH GH than in controls, although only 24S-hydroxycholesterol showed statistical significance (P<0.001). Cholesterol synthesis markers had a positive correlation with BMI, triglycerides, cholesterol and apoB in control population. However, these correlations disappeared in non-FH GH with the exception of a weak positive correlation for non-HDL cholesterol and apoB. The same pattern was observed for oxysterols with high positive correlation in controls and absence of correlation for non-FH GH, except non-HDL cholesterol for 24S-hydroxycholesterol and 27-hydroxycholesterol and apoB for 27-hydroxycholesterol. All non-cholesterol sterols had positive correlation among them in patients and in controls. A total of 65 (32.5%) and 35 (17.5%) affected subjects presented values of oxysterols ratios to total cholesterol above the 95th percentile of the normal distribution (24S-hydroxycholesterol and 27-hydroxycholesterol, respectively). Those patients with the highest levels of 24S-hydroxycholesterol associated an increase in the carotid intima media thickness. These results suggest that bile acid metabolism is affected in some patients with primary hypercholesterolemia of genetic origin, negative for mutations in the candidate genes, and may confer a higher cardiovascular risk. Our results confirm that cholesterol synthesis overproduction is a primary defect in non-HF GH and suggest that subjects with non-FH GH show high levels of oxysterols in response to hepatic overproduction of cholesterol.

Individualized Medicine in Gastroenterology and Hepatology

After the completion of the Human Genome Project, there has been an acceleration in methodologies on sequencing nucleic acids (DNA and RNA) at a high precision and with ever-decreasing turnaround time and cost. Collectively, these approaches are termed next-generation sequencing and are already affecting the transformation of medical practice. In this symposium article, we highlight the current knowledge of the genetics of selected gastrointestinal tract and liver diseases, namely, inflammatory bowel disease, hereditary cholestatic liver disease, and familial colon cancer syndromes. In addition, we provide a stepwise approach to use next-generation sequencing methodologies for clinical practice with the goal to improve the diagnosis as well as management of and/or therapy of the chosen digestive diseases. This early experience of applying next-generation sequencing in the practice of gastroenterology and hepatology will delineate future best practices in the field, ultimately for the benefit of our patients.

Bile acid analysis in human disorders of bile acid biosynthesis

Bile acids facilitate the absorption of lipids in the gut, but are also needed to maintain cholesterol homeostasis, induce bile flow, excrete toxic substances and regulate energy metabolism by acting as signaling molecules. Bile acid biosynthesis is a complex process distributed across many cellular organelles and requires at least 17 enzymes in addition to different metabolite transport proteins to synthesize the two primary bile acids, cholic acid and chenodeoxycholic acid. Disorders of bile acid synthesis can present from the neonatal period to adulthood and have very diverse clinical symptoms ranging from cholestatic liver disease to neuropsychiatric symptoms and spastic paraplegias. This review describes the different bile acid synthesis pathways followed by a summary of the current knowledge on hereditary disorders of human bile acid biosynthesis with a special focus on diagnostic bile acid profiling using mass spectrometry.

Genetic profiling of children with advanced cholestatic liver disease

Advanced cholestatic liver disease is a leading referral to pediatric liver transplant centers. Recent advances in the genetic classification of this group of disorders promise a highly personalized management although the genetic heterogeneity also poses a diagnostic challenge. Using a next-generation sequencing-based multi-gene panel, we performed retrospective analysis of 98 pediatric patients who presented with advanced cholestatic liver disease. A likely causal mutation was identified in the majority (61%), spanning many genes including ones that have only rarely been reported to cause cholestatic liver disease, e.g. TJP2 and VIPAS39. We find no evidence to support mono-allelic phenotypic expression in the carrier parents despite the severe nature of the respective mutations, and no evidence of oligogenicity. The high-carrier frequency of the founder mutations identified in our cohort (1 in 87) suggests a minimum incidence of 1:7246, an alarmingly high disease burden that calls for the primary prevention through carrier screening.

Guideline for the Evaluation of Cholestatic Jaundice in Infants: Joint Recommendations of the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition and the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition

Cholestatic jaundice in infancy affects approximately 1 in every 2500 term infants and is infrequently recognized by primary providers in the setting of physiologic jaundice. Cholestatic jaundice is always pathologic and indicates hepatobiliary dysfunction. Early detection by the primary care physician and timely referrals to the pediatric gastroenterologist/hepatologist are important contributors to optimal treatment and prognosis. The most common causes of cholestatic jaundice in the first months of life are biliary atresia (25%-40%) followed by an expanding list of monogenic disorders (25%), along with many unknown or multifactorial (eg, parenteral nutrition-related) causes, each of which may have time-sensitive and distinct treatment plans. Thus, these guidelines can have an essential role for the evaluation of neonatal cholestasis to optimize care. The recommendations from this clinical practice guideline are based upon review and analysis of published literature and the combined experience of the authors. The committee recommends that any infant noted to be jaundiced after 2 weeks of age be evaluated for cholestasis with measurement of total and direct serum bilirubin, and that an elevated serum direct bilirubin level (direct bilirubin levels >1.0 mg/dL or >17 μmol/L) warrants timely consideration for evaluation and referral to a pediatric gastroenterologist or hepatologist. Of note, current differential diagnostic plans now incorporate consideration of modern broad-based next-generation DNA sequencing technologies in the proper clinical context. These recommendations are a general guideline and are not intended as a substitute for clinical judgment or as a protocol for the care of all infants with cholestasis. Broad implementation of these recommendations is expected to reduce the time to the diagnosis of pediatric liver diseases, including biliary atresia, leading to improved outcomes.

Oxysterols: From cholesterol metabolites to key mediators

Oxysterols are cholesterol metabolites that can be produced through enzymatic or radical processes. They constitute a large family of lipids (i.e. the oxysterome) involved in a plethora of physiological processes. They can act through GPCR (e.g. EBI2, SMO, CXCR2), nuclear receptors (LXR, ROR, ERα) and through transporters or regulatory proteins. Their physiological effects encompass cholesterol, lipid and glucose homeostasis. Additionally, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis. First studied as precursors of bile acids, they quickly emerged as interesting lipid mediators. Their levels are greatly altered in several pathologies and some oxysterols (e.g. 4β-hydroxycholesterol or 7α-hydroxycholestenone) are used as biomarkers of specific pathologies. In this review, we discuss the complex metabolism and molecular targets (including binding properties) of these bioactive lipids in human and mice. We also discuss the genetic mouse models currently available to interrogate their effects in pathophysiological settings. We also summarize the levels of oxysterols reported in two key organs in oxysterol metabolism (liver and brain), plasma and cerebrospinal fluid. Finally, we consider future opportunities and directions in the oxysterol field in order to gain a better insight and understanding of the complex oxysterol system.

Tandem Mass Spectrometric Determination of Atypical 3β-Hydroxy-Δ5-Bile Acids in Patients with 3β-Hydroxy-Δ5-C27-Steroid Oxidoreductase Deficiency: Application to Diagnosis and Monitoring of Bile Acid Therapeutic Response

BACKGROUND

3β-Hydroxy-Δ5-C27-steroid oxidoreductase (HSD3B7) deficiency, a progressive cholestatic liver disease, is the most common genetic defect in bile acid synthesis. Early diagnosis is important because patients respond to oral primary bile acid therapy, which targets the negative feedback regulation for bile acid synthesis to reduce the production of hepatotoxic 3β-hydroxy-Δ5-bile acids. These atypical bile acids are highly labile and difficult to accurately measure, yet a method for accurate determination of 3β-hydroxy-Δ5-bile acid sulfates is critical for dose titration and monitoring response to therapy.

METHODS

We describe a electrospray ionization LC-MS/MS method for the direct measurement of atypical 3β-hydroxy-Δ5-bile acid sulfates in urine from patients with HSD3B7 deficiency that overcomes the deficiencies of previously used GC-MS methods.

RESULTS

Separation of sulfated 3β-hydroxy-Δ5-bile acids was achieved by reversed-phase HPLC in a 12-min analytical run. The mean (SE) urinary concentration of the total 3β-sulfated-Δ5-cholenoic acids in patients with HSD3B7 deficiency was 4650 (1711) μmol/L, approximately 1000-fold higher than in noncholestatic and cholestatic patients with intact primary bile acid synthesis. GC-MS was not reliable for measuring 3β-hydroxy-Δ5-bile acid sulfates; however, direct analysis of urine by fast atom bombardment mass spectrometry yielded meaningful semiquantitative assessment of urinary excretion.

CONCLUSIONS

The tandem mass spectrometry method described here for the measurement of 3β-hydroxy-Δ5-bile acid sulfates in urine can be applied to the diagnosis and accurate monitoring of responses to primary bile acid therapy in HSD3B7 patients.

Focused metabolomics using liquid chromatography/electrospray ionization tandem mass spectrometry for analysis of urinary conjugated cholesterol metabolites from patients with Niemann-Pick disease type C and 3β-hydroxysteroid dehydrogenase deficiency

BACKGROUND

Various conjugated cholesterol metabolites are excreted in urine of the patients with metabolic abnormalities and hepatobiliary diseases. We aimed to examine the usefulness of precursor ion scan and neutral loss scan for the characterization of conjugated cholesterol metabolites in urine.

METHODS

A mixture of authentic standards of conjugated cholesterol metabolites was used for investigating the performance of the present method. The urine of patients with Niemann-Pick diseases type C and 3β-hydroxysteroid dehydrogenase deficiency were analysed by precursor ion scan of m/z 97, 74, and 124.

RESULTS

A precursor ion scan of m/z 97 was effective for identifying conjugates with ester sulphates on hydroxyl groups whereas ester sulphates on phenolic alcohols were signalled by a neutral loss scan of 80 Da. Monosaccharide-conjugated cholesterol metabolites were signalled by a precursor ion scan of m/z 113. Although precursor ion scan of m/z 74 and 124 was effective for finding glycine- and taurine-conjugated metabolites, high intensity of product ions (m/z 74 and 124) disturbed measurement of other multiply conjugated metabolites. The urine samples contained many conjugated cholesterol metabolites, and there were several disease-specific intense peaks. We found several unknown intense peaks with three known peaks in urine of the Niemann-Pick type C patient. In the patient with 3β-hydroxysteroid dehydrogenase deficiency, intense peaks that were tentatively identified as 5-cholenoic acid sulphates and their glycine and taurine conjugates were present.

CONCLUSION

The method should lead to the discovery of new urinary biomarkers for these disturbances of cholesterol catabolism and transport.

25-Hydroxycholesterols in innate and adaptive immunity

Cholesterol and components of the cholesterol biosynthetic pathway have fundamental roles in all mammalian cells. Hydroxylated forms of cholesterol are now emerging as important regulators of immune function. This involves effects on the cholesterol biosynthetic pathway and cell membrane properties, which can have antiviral and anti-inflammatory influences. In addition, a dihydroxylated form of cholesterol functions as an immune cell guidance cue by engaging the G protein-coupled receptor EBI2, and it is required for mounting adaptive immune responses. In this Review, we summarize the current understanding of the closely related oxysterols 25-hydroxycholesterol and 7α,25-dihydroxycholesterol, and the growing evidence that they have wide-ranging influences on innate and adaptive immunity.

Genetic, anatomic, and clinical determinants of human serum sterol and vitamin D levels

An unknown fraction of the genome participates in the metabolism of sterols and vitamin D, two classes of lipids with diverse physiological and pathophysiological roles. Here, we used mass spectrometry to measure the abundance of >60 sterol and vitamin D derivatives in 3,230 serum samples from a well-phenotyped patient population. Twenty-nine of these lipids were detected in a majority of samples at levels that varied over thousands of fold in different individuals. Pairwise correlations between sterol and vitamin D levels revealed evidence for shared metabolic pathways, additional substrates for known enzymes, and transcriptional regulatory networks. Serum levels of multiple sterols and vitamin D metabolites varied significantly by sex, ethnicity, and age. A genome-wide association study identified 16 loci that were associated with levels of 19 sterols and 25-hydroxylated derivatives of vitamin D (P < 10(-7)). Resequencing, expression analysis, and biochemical experiments focused on one such locus (CYP39A1), revealed multiple loss-of-function alleles with additive effects on serum levels of the oxysterol, 24S-hydroxycholesterol, a substrate of the encoded enzyme. Body mass index, serum lipid levels, and hematocrit were strong phenotypic correlates of interindividual variation in multiple sterols and vitamin D metabolites. We conclude that correlating population-based analytical measurements with genotype and phenotype provides productive insight into human intermediary metabolism.

Bile acid metabolism and signaling

Bile acids are important physiological agents for intestinal nutrient absorption and biliary secretion of lipids, toxic metabolites, and xenobiotics. Bile acids also are signaling molecules and metabolic regulators that activate nuclear receptors and G protein-coupled receptor (GPCR) signaling to regulate hepatic lipid, glucose, and energy homeostasis and maintain metabolic homeostasis. Conversion of cholesterol to bile acids is critical for maintaining cholesterol homeostasis and preventing accumulation of cholesterol, triglycerides, and toxic metabolites, and injury in the liver and other organs. Enterohepatic circulation of bile acids from the liver to intestine and back to the liver plays a central role in nutrient absorption and distribution, and metabolic regulation and homeostasis. This physiological process is regulated by a complex membrane transport system in the liver and intestine regulated by nuclear receptors. Toxic bile acids may cause inflammation, apoptosis, and cell death. On the other hand, bile acid-activated nuclear and GPCR signaling protects against inflammation in liver, intestine, and macrophages. Disorders in bile acid metabolism cause cholestatic liver diseases, dyslipidemia, fatty liver diseases, cardiovascular diseases, and diabetes. Bile acids, bile acid derivatives, and bile acid sequestrants are therapeutic agents for treating chronic liver diseases, obesity, and diabetes in humans.

CCBE1 mutation in two siblings, one manifesting lymphedema-cholestasis syndrome, and the other, fetal hydrops

Background

Lymphedema-cholestasis syndrome (LCS; Aagenaes syndrome) is a rare autosomal recessive disorder, characterized by 1) neonatal intrahepatic cholestasis, often lessening and becoming intermittent with age, and 2) severe chronic lymphedema, mainly lower limb. LCS was originally described in a Norwegian kindred in which a locus, LCS1, was mapped to a 6.6cM region on chromosome 15. Mutations in CCBE1 on chromosome 18 have been reported in some cases of lymphatic dysplasia, but not in LCS.

Methods

Consanguineous parents of Mexican ancestry had a child with LCS who did not exhibit extended homozygosity in the LCS1 region. A subsequent pregnancy was electively terminated due to fetal hydrops. We performed whole-genome single nucleotide polymorphism genotyping to identify regions of homozygosity in these siblings, and sequenced promising candidate genes.

Results

Both siblings harbored a homozygous mutation in CCBE1, c.398 T>C, predicted to result in the missense change p.L133P. Regions containing known ‘cholestasis genes’ did not demonstrate homozygosity in the LCS patient.

Conclusions

Mutations in CCBE1 may yield a phenotype not only of lymphatic dysplasia, but also of LCS or fetal hydrops; however, the possibility that the sibling with LCS also carries a homozygous mutation in an unidentified gene influencing cholestasis cannot be excluded.

Oxysterol gradient generation by lymphoid stromal cells guides activated B cell movement during humoral responses

7α,25-dihydroxycholesterol (7α,25-OHC) is a ligand for the G protein-coupled receptor EBI2; however, the cellular sources of this oxysterol are undefined. 7α,25-OHC is synthesized from cholesterol by the stepwise actions of two enzymes, CH25H and CYP7B1, and is metabolized to a 3-oxo derivative by HSD3B7. We showed that all three enzymes control EBI2 ligand concentration in lymphoid tissues. Lymphoid stromal cells were the main CH25H- and CYP7B1-expressing cells required for positioning of B cells, and they also mediated 7α,25-OHC inactivation. CH25H and CYP7B1 were abundant at the follicle perimeter, whereas CH25H expression by follicular dendritic cells was repressed. CYP7B1, CH25H, and HSD3B7 deficiencies each resulted in defective T cell-dependent plasma cell responses. These findings establish that CYP7B1 and HSD3B7, as well as CH25H, have essential roles in controlling oxysterol production in lymphoid tissues, and they suggest that differential enzyme expression in stromal cell subsets establishes 7α,25-OHC gradients required for B cell responses.

Wx/ae double-mutant brown rice prevents the rise in plasma lipid and glucose levels in mice

A wx/ae double-mutant rice is generated by crossing waxy mutant and amylose-extender mutant in rice. Wx/ae brown rice contains highly beneficial nutrients for lipid and glucose metabolism, including resistant starch, dietary fiber, and γ-oryzanol, when compared to Koshihikari brown rice, the non-waxy japonica cultivar. To examine the effects of wx/ae brown rice on glucose and lipid metabolism, type 2 diabetic NSY/Hos mice were fed a high-fat diet containing 25% of wx/ae brown rice or Koshihikari brown rice for 10 weeks. The plasma total cholesterol, non-high-density lipoprotein cholesterol, triglyceride, and non-esterified fatty acid levels of the wx/ae group were significantly lower than those of the Koshihikari group. Moreover, the fasting blood glucose level and pathological score of glycosuria of the wx/ae group were also significantly lower than those of the Koshihikari group. These results indicate that wx/ae brown rice has the potential to prevent the rise in plasma lipid and glucose levels.

Utilization of metabolomics to identify serum biomarkers for hepatocellular carcinoma in patients with liver cirrhosis

Characterizing the metabolic changes pertaining to hepatocellular carcinoma (HCC) in patients with liver cirrhosis is believed to contribute towards early detection, treatment, and understanding of the molecular mechanisms of HCC. In this study, we compare metabolite levels in sera of 78 HCC cases with 184 cirrhotic controls by using ultra performance liquid chromatography coupled with a hybrid quadrupole time-of-flight mass spectrometry (UPLC-QTOF MS). Following data preprocessing, the most relevant ions in distinguishing HCC cases from patients with cirrhosis are selected by parametric and non-parametric statistical methods. Putative metabolite identifications for these ions are obtained through mass-based database search. Verification of the identities of selected metabolites is conducted by comparing their MS/MS fragmentation patterns and retention time with those from authentic compounds. Quantitation of these metabolites is performed in a subset of the serum samples (10 HCC and 10 cirrhosis) using isotope dilution by selected reaction monitoring (SRM) on triple quadrupole linear ion trap (QqQLIT) and triple quadrupole (QqQ) mass spectrometers. The results of this analysis confirm that metabolites involved in sphingolipid metabolism and phospholipid catabolism such as sphingosine-1-phosphate (S-1-P) and lysophosphatidylcholine (lysoPC 17:0) are up-regulated in sera of HCC vs. those with liver cirrhosis. Down-regulated metabolites include those involved in bile acid biosynthesis (specifically cholesterol metabolism) such as glycochenodeoxycholic acid 3-sulfate (3-sulfo-GCDCA), glycocholic acid (GCA), glycodeoxycholic acid (GDCA), taurocholic acid (TCA), and taurochenodeoxycholate (TCDCA). These results provide useful insights into HCC biomarker discovery utilizing metabolomics as an efficient and cost-effective platform. Our work shows that metabolomic profiling is a promising tool to identify candidate metabolic biomarkers for early detection of HCC cases in high risk population of cirrhotic patients.

Homozygosity mapping identifies a bile acid biosynthetic defect in an adult with cirrhosis of unknown etiology

The most common inborn error of bile acid metabolism is 3β-hydroxy-Δ(5)-C(27)-steroid oxidoreductase (3β-HSD) deficiency, a disorder that usually presents in early childhood with hepatic dysfunction. Timely diagnosis of this disorder is crucial because it can be effectively treated with primary bile acid replacement. Here we describe a 24-year-old woman from Iran with cirrhosis of unknown etiology. Her sister and a first cousin died of cirrhosis (ages 19 and 6 years) and another 32-year-old first cousin had a self-limited liver disorder in childhood that resolved at age 9 years. The family history suggested that the affected family members were homozygous for a mutant allele inherited identical-by-descent. A genome-wide analysis of 2.4 million single nucleotide polymorphisms was performed to identify regions of homozygosity that were present in the proband and the 32-year-old first cousin, but not in a healthy relative. One of these regions contained the gene encoding 3β-HSD (HSD3B7). Sequence analysis of HSD3B7 revealed that the proband and her 32-year-old cousin were homozygous for a frameshift mutation (c.45_46del AG, p.T15Tfsx27) in exon 1. The diagnosis of 3β-HSD deficiency was confirmed by documenting high levels of 3β-hydroxy-Δ(5) bile acids in the serum of the proband and the 32-year-old first cousin using mass spectrometry. To our knowledge, the 32-year-old relative in this family represents the oldest asymptomatic patient with this disorder.

CONCLUSION

This study highlights the clinical utility of homozygosity mapping in diagnosing autosomal recessive metabolic disorders. This family illustrates the wide variation in expressivity that occurs in 3β-HSD deficiency and underscores the need to consider a bile acid synthetic defect as a possible cause of liver disease in adults.

Five decades with oxysterols

I have been involved in research on oxysterols since 1963 and this review is intended to cover some of the most important aspects of this work. The first project dealed with 7α-hydroxy-4-cholesten-3-one. My successful synthesis of this steroid with high specific radioactivity allowed a demonstration that it is a bile acid precursor. The mechanism of conversion of 7α-hydroxycholesterol into 7α-hydroxy-4-cholesten-3-one was investigated and I concluded that only one enzyme is required and that no isomerase is involved. Accumulation of 7α-hydroxy-4-cholesten-3-one in patients with lack of sterol 27-hydroxylase (Cerebrotendinous xanthomatosis was shown to be an important pathogenetic factor. This disease is characterized by cholestanol-containing xanthomas in tendons and brain and we could show that most of this cholestanol is formed from 7α-hydroxy-4-cholesten-3-one. We also showed that 7α-hydroxy-4-cholesten-3-one passes the blood-brain barrier. In contrast to cholesterol itself, side-chain oxidized oxysterols have a high capacity to pass lipophilic membranes. We demonstrated conversion of cholesterol into 27-hydroxycholesterol to be a significant mechanism for elimination of cholesterol from macrophages. We also showed that conversion of cholesterol into 24S-hydroxycholesterol is important for elimination of cholesterol from the brain. Side-chain oxidized oxysterols have a high capacity to affect critical genes in cholesterol turnover in vitro. Most of the published in vitro experiments with oxysteroids are highly unphysiological, however. Mouse models studied in my laboratory with high or low levels of 27-hydroxycholesterol have little or no disturbances in cholesterol homeostasis. 24S-hydroxycholesterol is an efficient ligand to LXR and suggested to be important for cholesterol homeostasis in the brain. We recently developed a mouse model with markedly increased levels of this oxysterol in circulation and brain. This overexpression had however only a very modest effect on cholesterol turnover. We concluded that oxysterols are not the master regulators of cholesterol homeostasis in vivo suggested previously.

Expression of SLCO1B3 is associated with intratumoral cholestasis and CTNNB1 mutations in hepatocellular carcinoma

Recent studies have shown that intratumoral cholestasis is a hallmark of CTNNB1 mutations in hepatocellular carcinomas (HCC). Here, we analyzed the expressions of genes involved in bile acid and bilirubin metabolism and their correlation with the mutational status of CTNNB1 in a series of HCC. The expressions of CYP7A1 and CYP27A1, which encode rate-limiting enzymes in bile acid synthesis, were unaltered or only marginally increased in CTNNB1-mutated HCC compared with those in HCC with wild-type CTNNB1. Among the genes involved in bile acid and bilirubin transport, the expression of SLCO1B3 was significantly elevated in HCC with CTNNB1 mutations, whereas the expression of ABCC4 was elevated in HCC with wild-type CTNNB1. Immunohistochemistry confirmed the frequent expression of SLCO1B3 in CTNNB1-mutated HCC at the protein level, but not in most HCC with wild-type CTNNB1. Immunohistochemistry for MRP4 (encoded by ABCC4) partly agreed with ABCC4 expression, but most cases did not express detectable levels of MRP4. Notably, all HCC with bile accumulation, including those without CTNNB1 mutations, expressed SLCO1B3, suggesting that SLCO1B3 expression, rather than CTNNB1 mutation, is the critical determinant of intratumoral cholestasis. As SLCO1B3 is involved in the uptake of a number of chemotherapeutic and diagnostic agents, SLCO1B3 expression and the status of CTNNB1 mutation might need to be considered in the drug delivery to HCC.

Disorders of bile acid synthesis

Inborn errors of bile acid synthesis can produce life-threatening cholestatic liver disease (which usually presents in infancy) and progressive neurological disease presenting later in childhood or in adult life. Both types of disease can often be treated very effectively with bile acid replacement therapy and it is therefore important to diagnose these disorders as early as possible. The cholestatic disease in infancy is characterised by conjugated hyperbilirubinaemia with raised transaminases but normal γ-glutamyl transpeptidase and a biopsy showing a giant cell hepatitis. There is usually evidence of fat-soluble vitamin malabsorption. The neurological presentation often includes signs of upper motor neurone damage (spastic paraparesis). The most useful screening test for many of these disorders is analysis of urinary cholanoids (bile acids and bile alcohols); this is usually now achieved by electrospray ionisation tandem mass spectrometry. The disorders that are discussed in this review are: 3β-hydroxysteroid-Δ5-C27-steroid dehydrogenase deficiency, Δ4-3-oxosteroid 5β-reductase deficiency, sterol 27-hydroxylase deficiency (cerberotendinous xanthomatosis, CTX), oxysterol 7α-hydroxylase deficiency (including one form of hereditary spastic paraparesis) and the amidation defects, bile acid-CoA: aminoacid N-acyltransferase (BAAT) deficiency and bile acid-CoA ligase deficiency. The disorders of peroxisome biogenesis and peroxisomal β-oxidation that affect bile acid synthesis will be covered in the review by Ferdinandusse et al.

Biopsy Diagnosis of Inherited Liver Disease

Hepatic dysfunction during childhood can be due to acquired or inherited etiologies or a combination. The distinction can be difficult to make on liver biopsy, because the inherited disorders are rare and often lack pathognomonic light microscopic features. Recent progress in understanding the pathogenesis of these disorders has led to advances in molecular genetic screening and confirmatory tests. For a majority of these disorders, the liver biopsy continues to play a crucial role in primary diagnosis or confirmation. This article discusses algorithms that may aid pathologists in differential diagnosis of common inherited disorders of the liver, with emphasis on ancillary diagnostic tools and reference assays that are critical in establishing the diagnosis.

Molecular genetic and bile acid profiles in two Japanese patients with 3beta-hydroxy-DELTA5-C27-steroid dehydrogenase/isomerase deficiency

We report definitive diagnosis and effective chenodeoxycholic acid (CDCA) treatment of two Japanese children with 3[beta]-hydroxy-[DELTA]5-C27-steroid dehydrogenase/isomerase deficiency. Findings of cholestasis with normal serum [gamma]-glutamyltransferase activity and total bile acid concentration indicated the need for definitive bile acid analysis. Large amounts of 3[beta]-hydroxy-[DELTA]5 bile acids were detected by gas chromatography-mass spectrometry. HSD3B7 gene analysis using peripheral lymphocyte genomic DNA from the patients and their parents identified four novel mutations of the HSD3B7 gene in the patients. One had a homozygous mutation, 314delA; the other had compound heterozygous mutations: V132F, T149I, and 973_974insCCTGC. Interestingly, the second patient's mother had V132F and T149I mutations in one allele. Excessive 3[beta]-hydroxy-[DELTA]5-bile acids such as 3[beta],7[alpha]-dihydroxy- and 3[beta],7[alpha],12[alpha]-trihydroxy-5-cholenoic acids were detected in the first patient's urine; the second patient's urine contained large amounts of 3[beta]-hydroxy-5-cholenoic acid. Liver dysfunction in both patients decreased with ursodeoxycholic acid treatment, but unusual bile acids were still detected. Normalization of the patients' liver function and improvement of bile acid profiles occurred with CDCA treatment. Thus, we found mutations in the HSD3B7 gene accounting for autosomal recessive neonatal cholestasis caused by 3[beta]-hydroxy-[DELTA]5-C27-steroid dehydrogenase/isomerase deficiency. Early neonatal diagnosis permits initiation of CDCA treatment at this critical time, before the late cholestatic stage.

Genomic and neural analysis of the estradiol-synthetic pathway in the zebra finch

Background

Steroids are small molecule hormones derived from cholesterol. Steroids affect many tissues, including the brain. In the zebra finch, estrogenic steroids are particularly interesting because they masculinize the neural circuit that controls singing and their synthesis in the brain is modulated by experience. Here, we analyzed the zebra finch genome assembly to assess the content, conservation, and organization of genes that code for components of the estrogen-synthetic pathway and steroid nuclear receptors. Based on these analyses, we also investigated neural expression of a cholesterol transport protein gene in the context of song neurobiology.

Results

We present sequence-based analysis of twenty steroid-related genes using the genome assembly and other resources. Generally, zebra finch genes showed high homology to genes in other species. The diversity of steroidogenic enzymes and receptors may be lower in songbirds than in mammals; we were unable to identify all known mammalian isoforms of the 3β-hydroxysteroid dehydrogenase and 17β-hydroxysteroid dehydrogenase families in the zebra finch genome assembly, and not all splice sites described in mammals were identified in the corresponding zebra finch genes. We did identify two factors, Nobox and NR1H2-RXR, that may be important for coordinated transcription of multiple steroid-related genes. We found very little qualitative overlap in predicted transcription factor binding sites in the genes for two cholesterol transport proteins, the 18 kDa cholesterol transport protein (TSPO) and steroidogenic acute regulatory protein (StAR). We therefore performed in situ hybridization for TSPO and found that its mRNA was not always detected in brain regions where StAR and steroidogenic enzymes were previously shown to be expressed. Also, transcription of TSPO, but not StAR, may be regulated by the experience of hearing song.

Conclusions

The genes required for estradiol synthesis and action are represented in the zebra finch genome assembly, though the complement of steroidogenic genes may be smaller in birds than in mammals. Coordinated transcription of multiple steroidogenic genes is possible, but results were inconsistent with the hypothesis that StAR and TSPO mRNAs are co-regulated. Integration of genomic and neuroanatomical analyses will continue to provide insights into the evolution and function of steroidogenesis in the songbird brain.

Role of bile acids and bile acid receptors in metabolic regulation

The incidence of the metabolic syndrome has taken epidemic proportions in the past decades, contributing to an increased risk of cardiovascular disease and diabetes. The metabolic syndrome can be defined as a cluster of cardiovascular disease risk factors including visceral obesity, insulin resistance, dyslipidemia, increased blood pressure, and hypercoagulability. The farnesoid X receptor (FXR) belongs to the superfamily of ligand-activated nuclear receptor transcription factors. FXR is activated by bile acids, and FXR-deficient (FXR(-/-)) mice display elevated serum levels of triglycerides and high-density lipoprotein cholesterol, demonstrating a critical role of FXR in lipid metabolism. In an opposite manner, activation of FXR by bile acids (BAs) or nonsteroidal synthetic FXR agonists lowers plasma triglycerides by a mechanism that may involve the repression of hepatic SREBP-1c expression and/or the modulation of glucose-induced lipogenic genes. A cross-talk between BA and glucose metabolism was recently identified, implicating both FXR-dependent and FXR-independent pathways. The first indication for a potential role of FXR in diabetes came from the observation that hepatic FXR expression is reduced in animal models of diabetes. While FXR(-/-) mice display both impaired glucose tolerance and decreased insulin sensitivity, activation of FXR improves hyperglycemia and dyslipidemia in vivo in diabetic mice. Finally, a recent report also indicates that BA may regulate energy expenditure in a FXR-independent manner in mice, via activation of the G protein-coupled receptor TGR5. Taken together, these findings suggest that modulation of FXR activity and BA metabolism may open new attractive pharmacological approaches for the treatment of the metabolic syndrome and type 2 diabetes.

Medium- and short-chain dehydrogenase/reductase gene and protein families : the SDR superfamily: functional and structural diversity within a family of metabolic and regulatory enzymes

Short-chain dehydrogenases/reductases (SDRs) constitute a large family of NAD(P)(H)-dependent oxidoreductases, sharing sequence motifs and displaying similar mechanisms. SDR enzymes have critical roles in lipid, amino acid, carbohydrate, cofactor, hormone and xenobiotic metabolism as well as in redox sensor mechanisms. Sequence identities are low, and the most conserved feature is an α/β folding pattern with a central beta sheet flanked by 2–3 α-helices from each side, thus a classical Rossmannfold motif for nucleotide binding. The conservation of this element and an active site, often with an Asn-Ser-Tyr-Lys tetrad, provides a platform for enzymatic activities encompassing several EC classes, including oxidoreductases, epimerases and lyases. The common mechanism is an underlying hydride and proton transfer involving the nicotinamide and typically an active site tyrosine residue, whereas substrate specificity is determined by a variable C-terminal segment. Relationships exist with bacterial haloalcohol dehalogenases, which lack cofactor binding but have the active site architecture, emphasizing the versatility of the basic fold in also generating hydride transfer-independent lyases. The conserved fold and nucleotide binding emphasize the role of SDRs as scaffolds for an NAD(P)(H) redox sensor system, of importance to control metabolic routes, transcription and signalling.

Bile Acid sulfation: a pathway of bile acid elimination and detoxification

Sulfotransferase-2A1 catalyzes the formation of bile acid-sulfates (BA-sulfates). Sulfation of BAs increases their solubility, decreases their intestinal absorption, and enhances their fecal and urinary excretion. BA-sulfates are also less toxic than their unsulfated counterparts. Therefore, sulfation is an important detoxification pathway of BAs. Major species differences in BA sulfation exist. In humans, only a small proportion of BAs in bile and serum are sulfated, whereas more than 70% of BAs in urine are sulfated, indicating their efficient elimination in urine. The formation of BA-sulfates increases during cholestatic diseases. Therefore, sulfation may play an important role in maintaining BA homeostasis under pathologic conditions. Farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor are potential nuclear receptors that may be involved in the regulation of BA sulfation. This review highlights current knowledge about the enzymes and transporters involved in the formation and elimination of BA-sulfates, the effect of sulfation on the pharmacologic and toxicologic properties of BAs, the role of BA sulfation in cholestatic diseases, and the regulation of BA sulfation.

Genetic identification of HSD-1, a conserved steroidogenic enzyme that directs larval development inCaenorhabditis elegans

In C. elegans, steroid hormones function in conjunction with insulin/IGF-1-like signaling in promoting reproductive development over entry into the diapausal dauer stage. The NCR-1 and -2 (NPC1-related) intracellular cholesterol transporters function redundantly in preventing dauer arrest,presumably by regulating the availability of substrates for steroid hormone synthesis. We have identified hsd-1 as a new component of this cholesterol trafficking/processing pathway, using an ncr-1 enhancer screen. HSD-1 is orthologous to 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerases(3β-HSDs), which are key steroidogenic enzymes in vertebrates, and is exclusively expressed in two neuron-like XXX cells that are crucial in preventing dauer arrest, suggesting that it is involved in biosynthesis of dauer-preventing steroid hormones. The hsd-1 null mutant displays defects in inhibiting dauer arrest: it forms dauers in the deletion mutant backgrounds of ncr-1 or daf-28/insulin; as a single mutant,it is hypersensitive to dauer pheromone. We found that hsd-1 defects can be rescued by feeding mutant animals with several steroid intermediates that are either downstream of or in parallel to the 3β-HSD function in the dafachronic acid biosynthetic pathway, suggesting that HSD-1 functions as a 3β-HSD. Interestingly, sterols that rescued hsd-1 defects also bypassed the need for the NCR-1 and/or -2 functions, suggesting that HSD-1-mediated steroid hormone production is an important functional output of the NCR transporters. Finally, we found that the HSD-1-mediated signal activates insulin/IGF-I signaling in a cell non-autonomous fashion, suggesting a novel mechanism for how these two endocrine pathways intersect in directing development.

Mechanisms of disease: Inborn errors of bile acid synthesis

Inborn errors of bile acid synthesis are rare genetic disorders that can present as neonatal cholestasis, neurologic disease or fat-soluble-vitamin deficiencies. There are nine known defects of bile acid synthesis, including oxysterol 7alpha-hydroxylase deficiency, Delta(4)-3-oxosteroid-5beta-reductase deficiency, 3beta-hydroxy-Delta(5)-C(27)-steroid dehydrogenase deficiency, cerebrotendinous xanthomatosis (also known as sterol 27-hydroxylase deficiency), alpha-methylacyl-CoA racemase deficiency, and Zellweger syndrome (also known as cerebrohepatorenal syndrome). These diseases are characterized by a failure to produce normal bile acids and an accumulation of unusual bile acids and bile acid intermediaries. Individuals with inborn errors of bile acid synthesis generally present with the hallmark features of normal or low serum bile acid concentrations, normal gamma-glutamyl transpeptidase concentrations and the absence of pruritus. Failure to diagnose any of these conditions can result in liver failure or progressive chronic liver disease. If recognized early, many patients can have a remarkable clinical response to oral bile acid therapy.

Review article: The function and regulation of proteins involved in bile salt biosynthesis and transport

BACKGROUND

Bile salts are produced and secreted by the liver and are required for intestinal absorption of fatty food components and excretion of endobiotics and xenobiotics. They are reabsorbed in the terminal ileum and transported back to the liver via the portal tract. Dedicated bile salt transporters in hepatocytes and enterocytes are responsible for the unidirectional transport of bile salts in the enterohepatic cycle.

AIM

To give an overview of the function and regulations of proteins involved in bile salt synthesis and transport.

METHODS

Data presented are obtained from PubMed-accessible literature combined with our own recent research.

RESULT

Hepatocytes and enterocytes contain unique bile salt importers (sodium-taurocholate cotransporting polypeptide and apical sodium-dependent bile acid transporter, respectively) and exporters (bile salt export pump and organic solute transporter alpha-beta, respectively). Enzymes involved in bile salt biosynthesis reside in different subcellular locations, including the endoplasmic reticulum, mitochondria, cytosol and peroxisomes. Defective expression or function of the transporters or enzymes may lead to cholastasis. The bile salt-activated transcription factor Farnesoid X receptor controls expression of genes involved in bile salt biosynthesis and transport.

CONCLUSIONS

Detailed knowledge is available about the enzymes and transporters involved in bile salt homeostasis and how their defective function is associated with cholestasis. In contrast, the process of intracellular bile salt transport is largely unexplored.

Novel LC–MS/MS method for assay of 7α-hydroxy-4-cholesten-3-one in human plasma

A new isotope dilution LC-MS/MS method for assay of 7alpha-hydroxy-4-cholesten-3-one without need for derivatization is described. This method was used in catheterization experiments on healthy fasting volunteers. The levels of this generally used marker for bile acid synthesis were slightly but significantly higher in the hepatic vein than in the brachial artery. In contrast, the levels of the precursor to 7alpha-hydroxy-4 cholesten-3-one, 7alpha-hydroxycholesterol, were the same in the two vessels. It is concluded that there is a net extrahepatic metabolism of 7alpha-hydroxy-4-cholesten-3-one. The similarity and very high correlation between the levels in the two vessels (r=0.97) are consistent with the contention that 7alpha-hydroxy-4-cholesten-3-one is a suitable marker for the activity of the hepatic cholesterol 7alpha-hydroxylase and thus bile acid synthesis.

Cholestatic liver disease in adults may be due to an inherited defect in bile acid biosynthesis

BACKGROUND

An increasing number of treatable inborn errors of bile acid synthesis have been described, primarily in infants with severe cholestatic liver disease.

RESULTS

The present patient, whose two older siblings had died from progressive cholestatic liver disease, developed neonatal cholestasis and rickets but recovered during the childhood years and follow-up was terminated at 12 years of age. The patient presented again at 26 years of age with jaundice and pathological liver function tests. This was normalized upon treatment with ursodeoxycholic acid. Electrospray mass spectrometry of urine showed predominance of unsaturated bile acids, characteristic of 3beta-hydroxy-Delta5-C27-steroid dehydrogenase/isomerase (HSD3B7) deficiency. The activity of HSD3B7 in cultured fibroblasts was less than 5% of normal. A single homozygous mutation was found in exon 4 leading to an amino acid exchange (S162R) and loss of enzyme activity.

CONCLUSION

This case illustrates that infants with an inherited absence of HSD3B7 may survive the neonatal period of life and childhood without treatment with bile acids. A low level of sulphation of the abnormal trihydroxy bile acid formed as a result of enzyme deficiency may be of importance for survival. The possibility that liver disease presenting in the adult may be due to a mutation in the HSD3B7 gene should be considered, especially in cases with familial occurrence of liver disease and earlier periods of liver dysfunction.

Analysis of HSD3B7 knockout mice reveals that a 3alpha-hydroxyl stereochemistry is required for bile acid function

Primary bile acids are synthesized from cholesterol in the liver and thereafter are secreted into the bile and small intestine. Gut flora modify primary bile acids to produce secondary bile acids leading to a chemically diverse bile acid pool that is circulated between the small intestine and liver. A majority of primary and secondary bile acids in higher vertebrates have a 3alpha-hydroxyl group. Here, we characterize a line of knockout mice that cannot epimerize the 3beta-hydroxyl group of cholesterol and as a consequence synthesize a bile acid pool in which 3beta-hydroxylated bile acids predominate. This alteration causes death in 90% of newborn mice and decreases the absorption of dietary cholesterol in surviving adults. Negative feedback regulation of bile acid synthesis mediated by the farnesoid X receptor (FXR) is disrupted in the mutant mice. We conclude that the correct stereochemistry of a single hydroxyl group at carbon 3 in bile acids is required to maintain their physiologic and regulatory functions in mammals.

Genetics of familial intrahepatic cholestasis syndromes

Bile acids and bile salts have essential functions in the liver and in the small intestine. Their synthesis in the liver provides a metabolic pathway for the catabolism of cholesterol and their detergent properties promote the solubilisation of essential nutrients and vitamins in the small intestine. Inherited conditions that prevent the synthesis of bile acids or their excretion cause cholestasis, or impaired bile flow. These disorders generally lead to severe human liver disease, underscoring the essential role of bile acids in metabolism. Recent advances in the elucidation of gene defects underlying familial cholestasis syndromes has greatly increased knowledge about the process of bile flow. The expression of key proteins involved in bile flow is tightly regulated by transcription factors of the nuclear hormone receptor family, which function as sensors of bile acids and cholesterol. Here we review the genetics of familial cholestasis disorders, the functions of the affected genes in bile flow, and their regulation by bile acids and cholesterol.

Role of CYP27A in cholesterol and bile acid metabolism

The CYP27A gene encodes a mitochondrial cytochrome P450 enzyme, sterol 27-hydroxylase, that is expressed in many different tissues and plays an important role in cholesterol and bile acid metabolism. In humans, CYP27A deficiency leads to cerebrotendinous xanthomatosis. To gain insight into the roles of CYP27A in the regulation of cholesterol and bile acid metabolism, cyp27A gene knockout heterozygous, homozygous, and wild-type littermate mice were studied. In contrast to homozygotes, heterozygotes had increased body weight and were mildly hypercholesterolemic, with increased numbers of lipoprotein particles in the low density lipoprotein size range. Cyp7A expression was not increased in heterozygotes but was in homozygotes, suggesting that parts of the homozygous phenotype are secondary to increased cyp7A expression and activity. Homozygotes exhibited pronounced hepatomegaly and dysregulation in hepatic cholesterol, bile acid, and fatty acid metabolism. Hepatic cholesterol synthesis and synthesis of bile acid intermediates were increased; however, side chain cleavage was impaired, leading to decreased bile salt concentrations in gallbladder bile. Expression of Na-taurocholate cotransporting polypeptide, the major sinusoidal bile salt transporter, was increased, and that of bile salt export pump, the major canalicular bile salt transporter, was decreased. Gender played a modifying role in the homozygous response to cyp27A deficiency, with females being generally more severely affected. Thus, both cyp27A genotype and gender affected the regulation of hepatic bile acid, cholesterol, and fatty acid metabolism.