Targeting bile-acid signalling for metabolic diseases

Evolving therapies for non-alcoholic steatohepatitis

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the world. Approved therapies for this disorder, however, are still lacking. In the last decade, pathophysiological insights into this disease have been tremendous. Various aspects, such as insulin resistance, innate immunity, metabolic inflammation and the microbiota, have been characterized as major players. Indeed, at least 1 in 10 sufferers will have the disease escalate toward its inflammatory phenotype, non-alcoholic steatohepatitis (NASH). These pathways currently represent the most attractive treatment targets. Furthermore, interference with insulin resistance has shown some efficacy in the past, although more focused therapies, which also act anti-inflammatory, are needed.

AREAS COVERED

In this review, the authors highlight the current most promising treatment strategies in NASH/NAFLD.

EXPERT OPINION

Treatment of NAFLD is still in its infancy, although large controlled studies have demonstrated some efficacy for pioglitazone or vitamin E. The natural course of this disease demands long-term treatments besides diet and lifestyle changes. Based on the current view of NAFLD pathophysiology, effective therapies have to target metabolic inflammation, glucose and lipid metabolism. The search for agents interfering with all of these pathways has recently generated promising candidates for the treatment of NAFLD such as farnesoid X receptor, peroxisome proliferator-activated receptor-α/δ agonists or AdipoR small-molecule agonists.

In vivo performance of a novel fluorinated magnetic resonance imaging agent for functional analysis of bile acid transport

A novel trifluorinated cholic acid derivative, CA-lys-TFA, was designed and synthesized for use as a tool to measure bile acid transport noninvasively using magnetic resonance imaging (MRI). In the present study, the in vivo performance of CA-lys-TFA for measuring bile acid transport by MRI was investigated in mice. Gallbladder CA-lys-TFA content was quantified using MRI and liquid chromatography/tandem mass spectrometry. Results in wild-type (WT) C57BL/6J mice were compared to those in mice lacking expression of Asbt, the ileal bile acid transporter. (19)F signals emanating from the gallbladders of WT mice 7 h after oral gavage with 150 mg/kg CA-lys-TFA were reproducibly detected by MRI. Asbt-deficient mice administered the same dose had undetectable (19)F signals by MRI, and gallbladder bile CA-lys-TFA levels were 30-fold lower compared to WT animals. To our knowledge, this represents the first report of in vivo imaging of an orally absorbed drug using (19)F MRI. Fluorinated bile acid analogues have potential as tools to measure and detect abnormal bile acid transport by MRI.

FXR is a molecular target for the effects of vertical sleeve gastrectomy

Bariatric surgical procedures, such as vertical sleeve gastrectomy (VSG), are currently the most effective therapy for the treatment of obesity, and are associated with substantial improvements in co-morbidities, including type-2 diabetes mellitus. The underlying molecular mechanisms contributing to these benefits remain largely undetermined, despite offering tremendous potential to reveal new targets for therapeutic intervention. The present study demonstrates that the therapeutic value of VSG does not result from mechanical restriction imposed by a smaller stomach. Rather, we report that VSG is associated with increased circulating bile acids, and associated changes to gut microbial communities. Moreover, in the absence of nuclear bile acid receptor FXR, the ability of VSG to reduce body weight and improve glucose tolerance is substantially reduced. These results point to bile acids and FXR signaling as an important molecular underpinning for the beneficial effects of this weight-loss surgery.

Intercellular Lipid Mediators and GPCR Drug Discovery

G-protein-coupled receptors (GPCR) are the largest superfamily of receptors responsible for signaling between cells and tissues, and because they play important physiological roles in homeostasis, they are major drug targets. New technologies have been developed for the identification of new ligands, new GPCR functions, and for drug discovery purposes. In particular, intercellular lipid mediators, such as, lysophosphatidic acid and sphingosine 1-phosphate have attracted much attention for drug discovery and this has resulted in the development of fingolimod (FTY-720) and AM095. The discovery of new intercellular lipid mediators and their GPCRs are discussed from the perspective of drug development. Lipid GPCRs for lysophospholipids, including lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylcholine, free fatty acids, fatty acid derivatives, and other lipid mediators are reviewed.

Can medical therapy mimic the clinical efficacy or physiological effects of bariatric surgery?

The number of bariatric surgical procedures performed has increased dramatically. This review discusses the clinical and physiological changes, and in particular, the mechanisms behind weight loss and glycaemic improvements, observed following the gastric bypass, sleeve gastrectomy and gastric banding bariatric procedures. The review then examines how close we are to mimicking the clinical or physiological effects of surgery through less invasive and safer modern interventions that are currently available for clinical use. These include dietary interventions, orlistat, lorcaserin, phentermine/topiramate, glucagon-like peptide-1 receptor agonists, dipeptidyl peptidase-4 inhibitors, pramlintide, dapagliflozin, the duodenal-jejunal bypass liner, gastric pacemakers and gastric balloons. We conclude that, based on the most recent trials, we cannot fully mimic the clinical or physiological effects of surgery; however, we are getting closer. A 'medical bypass' may not be as far in the future as we previously thought, as the physician's armamentarium against obesity and type 2 diabetes has recently got stronger through the use of specific dietary modifications, novel medical devices and pharmacotherapy. Novel therapeutic targets include not only appetite but also taste/food preferences, energy expenditure, gut microbiota, bile acid signalling, inflammation, preservation of β-cell function and hepatic glucose output, among others. Although there are no magic bullets, an integrated multimodal approach may yield success. Non-surgical interventions that mimic the metabolic benefits of bariatric surgery, with a reduced morbidity and mortality burden, remain tenable alternatives for patients and health-care professionals.

Ostα-/- mice exhibit altered expression of intestinal lipid absorption genes, resistance to age-related weight gain, and modestly improved insulin sensitivity

The organic solute transporter OSTα-OSTβ is a key transporter for the efflux of bile acids across the basolateral membrane of ileocytes and the subsequent return of bile acids to the liver. Ostα(-/-) mice exhibit reduced bile acid pools and impaired lipid absorption. In this study, wild-type and Ostα(-/-) mice were characterized at 5 and 12 mo of age. Ostα(-/-) mice were resistant to age-related weight gain, body fat accumulation, and liver and muscle lipid accumulation, and male Ostα(-/-) mice lived slightly longer than wild-type mice. Caloric intake and activity levels were similar for Ostα(-/-) and wild-type male mice. Fecal lipid excretion was increased in Ostα(-/-) mice, indicating that a defect in lipid absorption contributes to decreased fat accumulation. Analysis of genes involved in intestinal lipid absorption revealed changes consistent with decreased dietary lipid absorption in Ostα(-/-) animals. Hepatic expression of cholesterol synthetic genes was upregulated in Ostα(-/-) mice, showing that increased cholesterol synthesis partially compensated for reduced dietary cholesterol absorption. Glucose tolerance was improved in male Ostα(-/-) mice, and insulin sensitivity was improved in male and female Ostα(-/-) mice. Akt phosphorylation was measured in liver and muscle tissue from mice after acute administration of insulin. Insulin responses were significantly larger in male and female Ostα(-/-) than wild-type mice. These findings indicate that loss of OSTα-OSTβ protects against age-related weight gain and insulin resistance.

FXR-dependent reduction of hepatic steatosis in a bile salt deficient mouse model

It has been established that bile salts play a role in the regulation of hepatic lipid metabolism. Accordingly, overt signs of steatosis have been observed in mice with reduced bile salt synthesis. The aim of this study was to identify the mechanism of hepatic steatosis in mice with bile salt deficiency due to a liver specific disruption of cytochrome P450 reductase. In this study mice lacking hepatic cytochrome P450 reductase (Hrn) or wild type (WT) mice were fed a diet supplemented with or without either 0.1% cholic acid (CA) or 0.025% obeticholic acid, a specific FXR-agonist. Feeding a CA-supplemented diet resulted in a significant decrease of plasma ALT in Hrn mice. Histologically, hepatic steatosis ameliorated after CA feeding and this was confirmed by reduced hepatic triglyceride content (115.5±7.3mg/g liver and 47.9±4.6mg/g liver in control- and CA-fed Hrn mice, respectively). The target genes of FXR-signaling were restored to normal levels in Hrn mice when fed cholic acid. VLDL secretion in both control and CA-fed Hrn mice was reduced by 25% compared to that in WT mice. In order to gain insight in the mechanism behind these bile salt effects, the FXR agonist also was administered for 3weeks. This resulted in a similar decrease in liver triglycerides, indicating that the effect seen in bile salt fed Hrn animals is FXR dependent. In conclusion, steatosis in Hrn mice is ameliorated when mice are fed bile salts. This effect is FXR dependent. Triglyceride accumulation in Hrn liver may partly involve impaired VLDL secretion.

Vitamin D and energy homeostasis: of mice and men

The vitamin D endocrine system has many extraskeletal targets, including adipose tissue. 1,25-Dihydroxyvitamin D₃, the active form of vitamin D, not only increases adipogenesis and the expression of typical adipocyte genes but also decreases the expression of uncoupling proteins. Mice with disrupted vitamin D action--owing to gene deletion of the nuclear receptor vitamin D receptor (Vdr) or the gene encoding 1α-hydroxylase (Cyp27b1)--lose fat mass over time owing to an increase in energy expenditure, whereas mice with increased Vdr-mediated signalling in adipose tissue become obese. The resistance to diet-induced obesity in mice with disrupted Vdr signalling is caused at least partially by increased expression of uncoupling proteins in white adipose tissue. However, the bile acid pool is also increased in these animals, and bile acids are known to be potent inducers of energy expenditure through activation of several nuclear receptors, including Vdr, and G-protein-coupled receptors, such as GPBAR1 (also known as TGR5). By contrast, in humans, obesity is strongly associated with poor vitamin D status. A causal link has not been firmly proven, but most intervention studies have failed to demonstrate a beneficial effect of vitamin D supplementation on body weight. The reasons for the major discrepancy between mouse and human data are unclear, but understanding the link between vitamin D status and energy homeostasis could potentially be very important for the human epidemic of obesity and the metabolic syndrome.

The human microbiome and bile acid metabolism: dysbiosis, dysmetabolism, disease and intervention

INTRODUCTION

Recent evidence indicates that the human gut microbiome plays a significant role in health and disease. Dysbiosis, defined as a pathological imbalance in a microbial community, is becoming increasingly appreciated as a 'central environmental factor' that is both associated with complex phenotypes and affected by host genetics, diet and antibiotic use. More recently, a link has been established between the dysmetabolism of bile acids (BAs) in the gut to dysbiosis.

AREAS COVERED

BAs, which are transformed by the gut microbiota, have been shown to regulate intestinal homeostasis and are recognized as signaling molecules in a wide range of metabolic processes. This review will examine the connection between BA metabolism as it relates to the gut microbiome and its implication in health and disease.

EXPERT OPINION

A disrupted gut microbiome, including a reduction of bile salt hydrolase (BSH)-active bacteria, can significantly impair the metabolism of BAs and may result in an inability to maintain glucose homeostasis as well as normal cholesterol breakdown and excretion. To better understand the link between dysbiosis, BA dysmetabolism and chronic degenerative disease, large-scale metagenomic sequencing studies, metatranscriptomics, metaproteomics and metabolomics should continue to catalog functional diversity in the gastrointestinal tract of both healthy and diseased populations. Further, BSH-active probiotics should continue to be explored as treatment options to help restore metabolic levels.

Farnesoid X receptor (FXR) gene deficiency impairs urine concentration in mice

The farnesoid X receptor (FXR) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily. FXR is mainly expressed in liver and small intestine, where it plays an important role in bile acid, lipid, and glucose metabolism. The kidney also has a high FXR expression level, with its physiological function unknown. Here we demonstrate that FXR is ubiquitously distributed in renal tubules. FXR agonist treatment significantly lowered urine volume and increased urine osmolality, whereas FXR knockout mice exhibited an impaired urine concentrating ability, which led to a polyuria phenotype. We further found that treatment of C57BL/6 mice with chenodeoxycholic acid, an FXR endogenous ligand, significantly up-regulated renal aquaporin 2 (AQP2) expression, whereas FXR gene deficiency markedly reduced AQP2 expression levels in the kidney. In vitro studies showed that the AQP2 gene promoter contained a putative FXR response element site, which can be bound and activated by FXR, resulting in a significant increase of AQP2 transcription in cultured primary inner medullary collecting duct cells. In conclusion, the present study demonstrates that FXR plays a critical role in the regulation of urine volume, and its activation increases urinary concentrating capacity mainly via up-regulating its target gene AQP2 expression in the collecting ducts.

Impact of new-generation lipid emulsions on cellular mechanisms of parenteral nutrition-associated liver disease

Parenteral nutrition (PN) is a life-saving nutritional support for a large population of hospitalized infants, and lipids make a substantial contribution to their energy and essential fatty acid (FA) needs. A challenge in the care of these infants is that their metabolic needs require prolonged PN support that increases the risk of PN-associated liver disease (PNALD). In recent years, the emergence of new parenteral lipid emulsions containing different source lipids and FA profiles has created nutritional alternatives to the first-generation, soybean oil-based lipid emulsion Intralipid. The limited U.S. introduction of the new-generation fish-oil emulsion Omegaven has generated promising results in infants with PNALD and spawned a renewed interest in how PN and lipid emulsions, in particular, contribute to this disease. Studies suggest that the lipid load and constituents, such as specific FAs, ratio of n-3 (ω-3) to n-6 (ω-6) long-chain polyunsaturated FAs, phytosterols, and vitamin E content, may be involved. There is an existing literature describing the molecular mechanisms whereby these specific nutrients affect hepatic metabolism and function via lipid and bile acid sensing nuclear receptors, such as peroxisome proliferator-activated receptor α, liver X receptor, and farnesoid X receptor, yet virtually no information as to how they interact and modulate liver function in the context of PN in pediatric patients or animal models. This article will review the recent development of parenteral lipid emulsions and their influence on PNALD and highlight some of the emerging molecular mechanisms that may explain the effects on liver function and disease.

O-GlcNAc: A Bittersweet Switch in Liver

The liver is a vital organ responsible for maintaining nutrient homeostasis. After a meal, insulin stimulates glycogen and lipid synthesis in the liver; in the fasted state, glucagon induces gluconeogenesis and ketogenesis, which produce glucose and ketone bodies for other tissues to use as energy sources. These metabolic changes involve spatiotemporally co-ordinated signaling cascades. O-linked β-N-acetylglucosamine (O-GlcNAc) modification has been recognized as a nutrient sensor and regulatory molecular switch. This review highlights mechanistic insights into spatiotemporal regulation of liver metabolism by O-GlcNAc modification and discusses its pathophysiological implications in insulin resistance, non-alcoholic fatty liver disease, and fibrosis.

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

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

Insights into lipidomic perturbations in zebrafish tissues upon exposure to microcystin-LR and microcystin-RR

This work represents the first study of its kind that was conducted to evaluate changes in lipid metabolic networks following a balneation exposure of adult zebrafish to MCLR (microcystin-leucine-arginine) and MCRR (microcystin-arginine-arginine) at a sublethal dose (10 μg L(-1)) for a period of 30 days. Following the exposure to MCLR and MCRR, gills, liver, intestine, and brain tissues were harvested for metabolite extraction. Extracted metabolites were detected using qTOF-LC-MS (time-of-flight-liquid chromatography-mass spectrometry). Metabolites were identified using Kegg pathways. The identified metabolites are shown on lipid biochemical maps to demonstrate major perturbations in the metabolic machinery. Results showed that most of the metabolic pathways under the lipid class were affected in different tissues of zebrafish following the exposure to MCLR and MCRR (10 μg L(-1) for 30 days). The kind and flux of metabolic perturbations varied among different tissues of the organs after the exposure to MCLR and MCRR with the tissues of gills being the most affected. Among the various lipid pathways, cholesterol synthesis was affected significantly as observed from the highest number of perturbed metabolites in that pathway. Cholesterol is responsible for synthesis of steroid hormones and bile acids, which have been recognized as endocrine signaling molecules. Disruption in the synthesis of these compounds following MCLR/MCRR exposure suggests that MCs are capable of causing endocrine disruption among aquatic organisms even under sublethal conditions. Apart from cholesterol synthesis, various other metabolic pathways belonging to the class of essential fatty acids and lipid oxidation were also observed to be perturbed following a balneation exposure of zebrafish to MCLR/MCRR.

Probing the Binding Site of Bile Acids in TGR5

TGR5 is a G-protein-coupled receptor (GPCR) mediating cellular responses to bile acids (BAs). Although some efforts have been devoted to generate homology models of TGR5 and draw structure-activity relationships of BAs, none of these studies has hitherto described how BAs bind to TGR5. Here, we present an integrated computational, chemical, and biological approach that has been instrumental to determine the binding mode of BAs to TGR5. As a result, key residues have been identified that are involved in mediating the binding of BAs to the receptor. Collectively, these results provide new hints to design potent and selective TGR5 agonists.

Human insulin resistance is associated with increased plasma levels of 12α-hydroxylated bile acids

Bile acids (BAs) exert pleiotropic metabolic effects, and physicochemical properties of different BAs affect their function. In rodents, insulin regulates BA composition, in part by regulating the BA 12α-hydroxylase CYP8B1. However, it is unclear whether a similar effect occurs in humans. To address this question, we examined the relationship between clamp-measured insulin sensitivity and plasma BA composition in a cohort of 200 healthy subjects and 35 type 2 diabetic (T2D) patients. In healthy subjects, insulin resistance (IR) was associated with increased 12α-hydroxylated BAs (cholic acid, deoxycholic acid, and their conjugated forms). Furthermore, ratios of 12α-hydroxylated/non-12α-hydroxylated BAs were associated with key features of IR, including higher insulin, proinsulin, glucose, glucagon, and triglyceride (TG) levels and lower HDL cholesterol. In T2D patients, BAs were nearly twofold elevated, and more hydrophobic, compared with healthy subjects, although we did not observe disproportionate increases in 12α-hydroxylated BAs. In multivariate analysis of the whole dataset, controlling for sex, age, BMI, and glucose tolerance status, higher 12α-hydroxy/non-12α-hydroxy BA ratios were associated with lower insulin sensitivity and higher plasma TGs. These findings suggest a role for 12α-hydroxylated BAs in metabolic abnormalities in the natural history of T2D and raise the possibility of developing insulin-sensitizing therapeutics based on manipulations of BA composition.

Bile acids and gut peptide secretion after bariatric surgery: a 1-year prospective randomized pilot trial

OBJECTIVE

Increased delivery of bile acid salts (BA) to distal L-cells and altered TGR5 receptor activation may contribute to the early and substantial increases in gut peptide secretion seen after bariatric surgery. To further elucidate a potential role of BA in the secretion of GLP-1 and PYY, we analyzed plasma BA concentrations in 14 morbidly obese patients undergoing gastric bypass or sleeve gastrectomy in a prospective, randomized 1-year trial.

DESIGN AND METHODS

Patients received a standard test meal and blood was collected before and after eating, prior to, and 1 week, 3 months, and 12 months after surgery.

RESULTS

Pre-surgery, basal BA concentrations were significantly lower in bariatric patients than in healthy controls. One year post-surgery, bariatric patients expressed variably increased BA concentrations (gastric bypass patients ∼2 fold increase, P ≤ 0.05). However, whereas in both patient groups, marked increases in GLP-1 and PYY and improved glycemic control was seen already 1 week and 3 months post-surgery, changes in plasma BA followed a different pattern: basal and postprandial plasma BA concentrations increased much slower, more progressively with significant increases only 1-year post-surgery.

CONCLUSIONS

Based on these findings, BA do not appear to be key mediators of the early increase in GLP-1 and PYY response in post-bariatric patients.

De novo synthesis of steroids and oxysterols in adipocytes

Local production and action of cholesterol metabolites such as steroids or oxysterols within endocrine tissues are currently recognized as an important principle in the cell type- and tissue-specific regulation of hormone effects. In adipocytes, one of the most abundant endocrine cells in the human body, the de novo production of steroids or oxysterols from cholesterol has not been examined. Here, we demonstrate that essential components of cholesterol transport and metabolism machinery in the initial steps of steroid and/or oxysterol biosynthesis pathways are present and active in adipocytes. The ability of adipocyte CYP11A1 in producing pregnenolone is demonstrated for the first time, rendering adipocyte a steroidogenic cell. The oxysterol 27-hydroxycholesterol (27HC), synthesized by the mitochondrial enzyme CYP27A1, was identified as one of the major de novo adipocyte products from cholesterol and its precursor mevalonate. Inhibition of CYP27A1 activity or knockdown and deletion of the Cyp27a1 gene induced adipocyte differentiation, suggesting a paracrine or autocrine biological significance for the adipocyte-derived 27HC. These findings suggest that the presence of the 27HC biosynthesis pathway in adipocytes may represent a defense mechanism to prevent the formation of new fat cells upon overfeeding with dietary cholesterol.

Bile acid-controlled transgene expression in mammalian cells and mice

In recent years, using trigger-inducible mammalian gene switches to design sophisticated transcription-control networks has become standard practice in synthetic biology. These switches provide unprecedented precision, complexity and reliability when programming novel mammalian cell functions. Metabolite-responsive repressors of human-pathogenic bacteria are particularly attractive for use in these orthogonal synthetic mammalian gene switches because the trigger compound sensitivity often matches the human physiological range. We have designed both a bile acid-repressible (BEAROFF) as well as a bile-acid-inducible (BEARON) gene switch by capitalizing on components that have evolved to manage bile acid resistance in Campylobacter jejuni, the leading causative agent of human food-borne enteritis. We have shown that both of these switches enable bile acid-adjustable transgene expression in different mammalian cell lines as well as in mice. For the BEAROFF device, the C. jejuni repressor CmeR was fused to the VP16 transactivation domain to create a synthetic transactivator that activates minimal promoters containing tandem operator modules (Ocme) in a bile acid-repressible manner. Fusion of CmeR to a transsilencing domain resulted in an artificial transsilencer that binds and represses a constitutive Ocme-containing promoter until it is released by addition of bile acid (BEARON). A tailored multi-step tuning program for the inducible gene switch, which included the optimization of individual component performance, control of their relative abundances, the choice of the cell line and trigger compound, resulted in a BEARON device with significantly improved bile acid-responsive control characteristics. Synthetic metabolite-triggered gene switches that are able to interface with host metabolism may foster advances in future gene and cell-based therapies.

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.

Retinoic acid-related orphan receptor α regulates diurnal rhythm and fasting induction of sterol 12α-hydroxylase in bile acid synthesis

Sterol 12α-hydroxylase (CYP8B1) is required for cholic acid synthesis and plays a critical role in intestinal cholesterol absorption and pathogenesis of cholesterol gallstone, dyslipidemia, and diabetes. In this study we investigated the underlying mechanism of fasting induction and circadian rhythm of CYP8B1 by a cholesterol-activated nuclear receptor and core clock gene retinoic acid-related orphan receptor α (RORα). Fasting stimulated, whereas restricted-feeding reduced expression of CYP8B1 mRNA and protein. However, fasting and feeding had little effect on the diurnal rhythm of RORα mRNA expression, but fasting increased RORα protein levels by cAMP-activated protein kinase A-mediated phosphorylation and stabilization of the protein. Adenovirus-mediated gene transduction of RORα to mice strongly induced CYP8B1 expression, and increased liver cholesterol and 12α-hydroxylated bile acids in the bile acid pool and serum. A reporter assay identified a functional RORα response element in the CYP8B1 promoter. RORα recruited cAMP response element-binding protein-binding protein (CBP) to stimulate histone acetylation on the CYP8B1 gene promoter. In conclusion, RORα is a key regulator of diurnal rhythm and fasting induction of CYP8B1, which regulates bile acid composition and serum and liver cholesterol levels. Antagonizing RORα activity may be a therapeutic strategy for treating inflammatory diseases such as non-alcoholic fatty liver disease and type 2 diabetes.

Commensal bacteria at the interface of host metabolism and the immune system

The mammalian gastrointestinal tract, the site of digestion and nutrient absorption, harbors trillions of beneficial commensal microbes from all three domains of life. Commensal bacteria, in particular, are key participants in the digestion of food, and are responsible for the extraction and synthesis of nutrients and other metabolites that are essential for the maintenance of mammalian health. Many of these nutrients and metabolites derived from commensal bacteria have been implicated in the development, homeostasis and function of the immune system, suggesting that commensal bacteria may influence host immunity via nutrient- and metabolite-dependent mechanisms. Here we review the current knowledge of how commensal bacteria regulate the production and bioavailability of immunomodulatory, diet-dependent nutrients and metabolites and discuss how these commensal bacteria-derived products may regulate the development and function of the mammalian immune system.

Nonalcoholic fatty liver disease: molecular pathways and therapeutic strategies

Along with rising numbers of patients with metabolic syndrome, the prevalence of nonalcoholic fatty liver disease (NAFLD) has increased in proportion with the obesity epidemic. While there are no established treatments for NAFLD, current research is targeting new molecular mechanisms that underlie NAFLD and associated metabolic disorders. This review discusses some of these emerging molecular mechanisms and their therapeutic implications for the treatment of NAFLD. The basic research that has identified potential molecular targets for pharmacotherapy will be outlined.

Structural and functional characterization of BaiA, an enzyme involved in secondary bile acid synthesis in human gut microbe

Despite significant influence of secondary bile acids on human health and disease, limited structural and biochemical information is available for the key gut microbial enzymes catalyzing its synthesis. Herein, we report apo- and cofactor bound crystal structures of BaiA2, a short chain dehydrogenase/reductase from Clostridium scindens VPI 12708 that represent the first protein structure of this pathway. The structures elucidated the basis of cofactor specificity and mechanism of proton relay. A conformational restriction involving Glu42 located in the cofactor binding site seems crucial in determining cofactor specificity. Limited flexibility of Glu42 results in imminent steric and electrostatic hindrance with 2'-phosphate group of NADP(H). Consistent with crystal structures, steady state kinetic characterization performed with both BaiA2 and BaiA1, a close homolog with 92% sequence identity, revealed specificity constant (kcat /KM ) of NADP(+) at least an order of magnitude lower than NAD(+) . Substitution of Glu42 with Ala improved specificity toward NADP(+) by 10-fold compared to wild type. The cofactor bound structure uncovered a novel nicotinamide-hydroxyl ion (NAD(+) -OH(-) ) adduct contraposing previously reported adducts. The OH(-) of the adduct in BaiA2 is distal to C4 atom of nicotinamide and proximal to 2'-hydroxyl group of the ribose moiety. Moreover, it is located at intermediary distances between terminal functional groups of active site residues Tyr157 (2.7 Å) and Lys161 (4.5 Å). Based on these observations, we propose an involvement of NAD(+) -OH(-) adduct in proton relay instead of hydride transfer as noted for previous adducts.

Mechanisms underlying weight loss after bariatric surgery

The clinical efficacy of bariatric surgery has encouraged the scientific investigation of the gut as a major endocrine organ. Manipulation of gastrointestinal anatomy through surgery has been shown to profoundly affect the physiological and metabolic processes that control body weight and glycaemia. The most popular bariatric surgical procedures are gastric bypass, adjustable gastric banding and vertical sleeve gastrectomy. Even though these procedures were designed with the aim of causing restriction of food intake and nutrient malabsorption, evidence suggests that their contributions to weight loss are minimal. Instead, these interventions reduce body weight by decreasing hunger, increasing satiation during a meal, changing food preferences and energy expenditure. In this Review, we have explored these mechanisms as well as their mediators. The hope is that that their in-depth investigation will enable the optimization and individualization of surgical techniques, the development of equally effective but safer nonsurgical weight-loss interventions, and even the understanding of the pathophysiology of obesity itself.

Target hopping as a useful tool for the identification of novel EphA2 protein-protein antagonists

Lithocholic acid (LCA), a physiological ligand for the nuclear receptor FXR and the G-protein-coupled receptor TGR5, has been recently described as an antagonist of the EphA2 receptor, a key member of the ephrin signalling system involved in tumour growth. Given the ability of LCA to recognize FXR, TGR5, and EphA2 receptors, we hypothesized that the structural requirements for a small molecule to bind each of these receptors might be similar. We therefore selected a set of commercially available FXR or TGR5 ligands and tested them for their ability to inhibit EphA2 by targeting the EphA2-ephrin-A1 interface. Among the selected compounds, the stilbene carboxylic acid GW4064 was identified as an effective antagonist of EphA2, being able to block EphA2 activation in prostate carcinoma cells, in the micromolar range. This finding proposes the "target hopping" approach as a new effective strategy to discover new protein-protein interaction inhibitors.

Efficacy and safety of the farnesoid X receptor agonist obeticholic acid in patients with type 2 diabetes and nonalcoholic fatty liver disease

BACKGROUND & AIMS

Obeticholic acid (OCA; INT-747, 6α-ethyl-chenodeoxycholic acid) is a semisynthetic derivative of the primary human bile acid chenodeoxycholic acid, the natural agonist of the farnesoid X receptor, which is a nuclear hormone receptor that regulates glucose and lipid metabolism. In animal models, OCA decreases insulin resistance and hepatic steatosis.

METHODS

We performed a double-blind, placebo-controlled, proof-of-concept study to evaluate the effects of OCA on insulin sensitivity in patients with nonalcoholic fatty liver disease and type 2 diabetes mellitus. Patients were randomly assigned to groups given placebo (n = 23), 25 mg OCA (n = 20), or 50 mg OCA (n = 21) once daily for 6 weeks. A 2-stage hyperinsulinemic-euglycemic insulin clamp was used to measure insulin sensitivity before and after the 6-week treatment period. We also measured levels of liver enzymes, lipid analytes, fibroblast growth factor 19, 7α-hydroxy-4-cholesten-3-one (a BA precursor), endogenous bile acids, and markers of liver fibrosis.

RESULTS

When patients were given a low-dose insulin infusion, insulin sensitivity increased by 28.0% from baseline in the group treated with 25 mg OCA (P = .019) and 20.1% from baseline in the group treated with 50 mg OCA (P = .060). Insulin sensitivity increased by 24.5% (P = .011) in combined OCA groups, whereas it decreased by 5.5% in the placebo group. A similar pattern was observed in patients given a high-dose insulin infusion. The OCA groups had significant reductions in levels of γ-glutamyltransferase and alanine aminotransferase and dose-related weight loss. They also had increased serum levels of low-density lipoprotein cholesterol and fibroblast growth factor 19, associated with decreased levels of 7α-hydroxy-4-cholesten-3-one and endogenous bile acids, indicating activation of farnesoid X receptor. Markers of liver fibrosis decreased significantly in the group treated with 25 mg OCA. Adverse experiences were similar among groups.

CONCLUSIONS

In this phase 2 trial, administration of 25 or 50 mg OCA for 6 weeks was well tolerated, increased insulin sensitivity, and reduced markers of liver inflammation and fibrosis in patients with type 2 diabetes mellitus and nonalcoholic fatty liver disease. Longer and larger studies are warranted. ClinicalTrials.gov, Number: NCT00501592.

Synthesis and quantitative structure-property relationships of side chain-modified hyodeoxycholic acid derivatives

Bile acids have emerged as versatile signalling compounds of a complex network of nuclear and membrane receptors regulating various endocrine and paracrine functions. The elucidation of the interconnection between the biological pathways under the bile acid control and manifestations of hepatic and metabolic diseases have extended the scope of this class of steroids for in vivo investigations. In this framework, the design and synthesis of novel biliary derivatives able to modulate a specific receptor requires a deep understanding of both structure-activity and structure-property relationships of bile acids. In this paper, we report the preparation and the critical micellization concentration evaluation of a series of hyodeoxycholic acid derivatives characterized by a diverse side chain length and by the presence of a methyl group at the alpha position with respect to the terminal carboxylic acid moiety. The data collected are instrumental to extend on a quantitative basis, the knowledge of the current structure-property relationships of bile acids and will be fruitful, in combination with models of receptor activity, to design and prioritize the synthesis of novel pharmacokinetically suitable ligands useful in the validation of bile acid-responsive receptors as therapeutic targets.

Bile acid receptors in non-alcoholic fatty liver disease

Accumulating data have shown that bile acids are important cell signaling molecules, which may activate several signaling pathways to regulate biological processes. Bile acids are endogenous ligands for the farnesoid X receptor (FXR) and TGR5, a G-protein coupled receptor. Gain- and loss-of-function studies have demonstrated that both FXR and TGR5 play important roles in regulating lipid and carbohydrate metabolism and inflammatory responses. Importantly, activation of FXR or TGR5 lowers hepatic triglyceride levels and inhibits inflammation. Such properties of FXR or TGR5 have indicated that these two bile acid receptors are ideal targets for treatment of non-alcoholic fatty liver disease, one of the major health concerns worldwide. In this article, we will focus on recent advances on the role of both FXR and TGR5 in regulating hepatic triglyceride metabolism and inflammatory responses under normal and disease conditions.

Bile acid signal-induced phosphorylation of small heterodimer partner by protein kinase Cζ is critical for epigenomic regulation of liver metabolic genes

Bile acids (BAs) are recently recognized key signaling molecules that control integrative metabolism and energy expenditure. BAs activate multiple signaling pathways, including those of nuclear receptors, primarily farnesoid X receptor (FXR), membrane BA receptors, and FXR-induced FGF19 to regulate the fed-state metabolism. Small heterodimer partner (SHP) has been implicated as a key mediator of these BA signaling pathways by recruitment of chromatin modifying proteins, but the key question of how SHP transduces BA signaling into repressive histone modifications at liver metabolic genes remains unknown. Here we show that protein kinase Cζ (PKCζ) is activated by BA or FGF19 and phosphorylates SHP at Thr-55 and that Thr-55 phosphorylation is critical for the epigenomic coordinator functions of SHP. PKCζ is coimmunopreciptitated with SHP and both are recruited to SHP target genes after bile acid or FGF19 treatment. Activated phosphorylated PKCζ and phosphorylated SHP are predominantly located in the nucleus after FGF19 treatment. Phosphorylation at Thr-55 is required for subsequent methylation at Arg-57, a naturally occurring mutation site in metabolic syndrome patients. Thr-55 phosphorylation increases interaction of SHP with chromatin modifiers and their occupancy at selective BA-responsive genes. This molecular cascade leads to repressive modifications of histones at metabolic target genes, and consequently, decreased BA pools and hepatic triglyceride levels. Remarkably, mutation of Thr-55 attenuates these SHP-mediated epigenomic and metabolic effects. This study identifies PKCζ as a novel key upstream regulator of BA-regulated SHP function, revealing the role of Thr-55 phosphorylation in epigenomic regulation of liver metabolism.

Bile acids induce apoptosis selectively in androgen-dependent and -independent prostate cancer cells

Prostate cancer is a prevalent age-related disease in North America, accounting for about 15% of all diagnosed cancers. We have previously identified lithocholic acid (LCA) as a potential chemotherapeutic compound that selectively kills neuroblastoma cells while sparing normal human neurons. Now, we report that LCA inhibits the proliferation of androgen-dependent (AD) LNCaP prostate cancer cells and that LCA is the most potent bile acid with respect to inducing apoptosis in LNCaP as well as androgen-independent (AI) PC-3 cells, without killing RWPE-1 immortalized normal prostate epithelial cells. In LNCaP and PC-3 cells, LCA triggered the extrinsic pathway of apoptosis and cell death induced by LCA was partially dependent on the activation of caspase-8 and -3. Moreover, LCA increased cleavage of Bid and Bax, down-regulation of Bcl-2, permeabilization of the mitochondrial outer membrane and activation of caspase-9. The cytotoxic actions of LCA occurred despite the inability of this bile acid to enter the prostate cancer cells with about 98% of the nominal test concentrations present in the extracellular culture medium. With our findings, we provide evidence to support a mechanism of action underlying the broad anticancer activity of LCA in various human tissues.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Genetic variation in aldo-keto reductase 1D1 (AKR1D1) affects the expression and activity of multiple cytochrome P450s

Human liver gene regulatory (Bayesian) network analysis was previously used to identify a cytochrome P450 (P450) gene subnetwork with Aldo-keto reductase 1D1 (AKR1D1) as a key regulatory driver of this subnetwork. This study assessed the biologic importance of AKR1D1 [a key enzyme in the synthesis of bile acids, ligand activators of farnesoid X receptor (FXR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR), known transcriptional regulators of P450s] to hepatic P450 expression. Overexpression of AKR1D1 in primary human hepatocytes led to increased expression of CYP3A4, CYP2C8, CYP2C9, CYP2C19, and CYP2B6. Conversely, AKR1D1 knockdown decreased expression of these P450s. We resequenced AKR1D1 from 98 donor livers and identified a 3'-untranslated region (UTR) (rs1872930) single nucleotide polymorphism (SNP) significantly associated with higher AKR1D1 mRNA expression. AKR1D1 3'-UTR-luciferase reporter studies showed that the variant allele resulted in higher luciferase activity, suggesting that the SNP increases AKR1D1 mRNA stability and/or translation efficiency. Consistent with AKR1D1's putative role as a driver of the P450 subnetwork, the AKR1D1 3'-UTR SNP was significantly associated with increased hepatic mRNA expression of multiple P450s (CYP3A4, CYP2C8, CYP2C9, CYP2C19, and CYP2B6) and CYP3A4, CYP2C8, CYP2C19, and CYP2B6 activities. After adjusting for multiple testing, the association remained significant for AKR1D1, CYP2C9, and CYP2C8 mRNA expression and CYP2C8 activity. These results provide new insights into the variation in expression and activity of P450s that can account for interindividual differences in drug metabolism/efficacy and adverse drug events. In conclusion, we provide the first experimental evidence supporting a role for AKR1D1 as a key genetic regulator of the P450 network.

An association between post-meal bile acid response and bone resorption in normal subjects

Background

The mechanism surrounding bone suppression after a meal may involve several mediators, but is yet to be clarified. Bile acids (BA) function as signalling molecules in response to feeding, and may be directly involved in bone suppression acutely after a meal. The aim of this study was to test the hypothesis that BA are involved in the acute bone suppression observed after a meal.

Methods

A prospective study in which samples collected from volunteers fed a 400 Kcal test meal after an overnight fast were analysed for parathyroid hormone (PTH), BA, and carboxyterminal of type 1 collagen telopeptide (CTX). The study was carried out in 10 healthy male volunteers. Ethical approval was obtained from the Local Research and Ethics Committee at King's College Hospital.

Results

Total BA, glycine conjugated bile acids (GCBA), PTH and CTX showed a response to meal ingestion. There was a negative correlation between percentage change in PTH and CTX ( R2 = −0.82, P = 0.004), and between PTH and GCBA ( R2 = −0.39, P = 0.005).

Conclusion

This study demonstrated an association between GCBA and PTH suppression after a meal. The drop in PTH concentration after a meal may be responsible for the suppression of bone resorption as observed by the decrease in CTX concentration.

Familial hypercholesterolemia and atherosclerosis in cloned minipigs created by DNA transposition of a human PCSK9 gain-of-function mutant

Lack of animal models with human-like size and pathology hampers translational research in atherosclerosis. Mouse models are missing central features of human atherosclerosis and are too small for intravascular procedures and imaging. Modeling the disease in minipigs may overcome these limitations, but it has proven difficult to induce rapid atherosclerosis in normal pigs by high-fat feeding alone, and genetically modified models similar to those created in mice are not available. D374Y gain-of-function mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene cause severe autosomal dominant hypercholesterolemia and accelerates atherosclerosis in humans. Using Sleeping Beauty DNA transposition and cloning by somatic cell nuclear transfer, we created Yucatan minipigs with liver-specific expression of human D374Y-PCSK9. D374Y-PCSK9 transgenic pigs displayed reduced hepatic low-density lipoprotein (LDL) receptor levels, impaired LDL clearance, severe hypercholesterolemia, and spontaneous development of progressive atherosclerotic lesions that could be visualized by noninvasive imaging. This model should prove useful for several types of translational research in atherosclerosis.

The bile acid membrane receptor TGR5: a novel pharmacological target in metabolic, inflammatory and neoplastic disorders

TGR5 is the G-protein-coupled bile acid-activated receptor, found in many human and animal tissues. Considering different endocrine and paracrine functions of bile acids, the current review focuses on the role of TGR5 as a novel pharmacological target in the metabolic syndrome and related disorders, such as diabetes, obesity, atherosclerosis, liver diseases and cancer. TGR5 ligands improve insulin sensitivity and glucose homeostasis through the secretion of incretins. The bile acid/TGR5/cAMP signaling pathway increases energy expenditure in brown adipose tissue and skeletal muscle. Activation of TGR5 in macrophages inhibits production of proinflammatory cytokines and attenuates the development of atherosclerosis. This receptor has been detected in many cell types of the liver where it has anti-inflammatory effects, thus reducing liver steatosis and damage. TGR5 also modulates hepatic microcirculation and fluid secretion in the biliary tree. In cell culture models TGR5 has been linked to signaling pathways involved in metabolism, cell survival, proliferation and apoptosis, which suggest a possible role of TGR5 in cancer development. Despite the fact that TGR5 ligands may represent novel drugs for prevention and treatment of different aspects of the metabolic syndrome, clinical studies are awaited with the perspective that they will complete TGR5 biology and identify efficient and safe TGR5 agonists.

Hyodeoxycholic acid improves HDL function and inhibits atherosclerotic lesion formation in LDLR-knockout mice

We examined the effects of a natural secondary bile acid, hyodeoxycholic acid (HDCA), on lipid metabolism and atherosclerosis in LDL receptor-null (LDLRKO) mice. Female LDLRKO mice were maintained on a Western diet for 8 wk and then divided into 2 groups that received chow, or chow + 1.25% HDCA, diets for 15 wk. We observed that mice fed the HDCA diet were leaner and exhibited a 37% (P<0.05) decrease in fasting plasma glucose level. HDCA supplementation significantly decreased atherosclerotic lesion size at the aortic root region, the entire aorta, and the innominate artery by 44% (P<0.0001), 48% (P<0.01), and 94% (P<0.01), respectively, as compared with the chow group. Plasma VLDL/IDL/LDL cholesterol levels were significantly decreased, by 61% (P<0.05), in the HDCA group as compared with the chow diet group. HDCA supplementation decreased intestinal cholesterol absorption by 76% (P<0.0001) as compared with the chow group. Furthermore, HDL isolated from the HDCA group exhibited significantly increased ability to mediate cholesterol efflux ex vivo as compared with HDL of the chow diet group. In addition, HDCA significantly increased the expression of genes involved in cholesterol efflux, such as Abca1, Abcg1, and Apoe, in a macrophage cell line. Thus, HDCA is a candidate for antiatherosclerotic drug therapy.

[Detailed characterization of bile acid and glucocorticoid world by mass spectrometry]

  The Nobel Prize in Chemistry for 2002 was shared by John B. Fenn and Koichi Tanaka "for their development of soft desorption methods for mass spectrometric analyses of biological macromolecules". Indeed, electrospray ionization and soft laser desorption ionization have proved to be of great value in "omics", such as metabolomics, transcriptomics and proteomics in providing a systematic and quantitative approach to the study of biological systems and networks. Moreover, these techniques have made great contributions to metabolic studies that are used for development of new drugs, as well as to the diagnosis of diseases including cancer based on the specific and sensitive detection of molecular biomarkers. In this article, we describe our recent results on characterization of bile acid metabolism in hepatobiliary disease as well as measurement of conjugated urinary tetrahydrocorticosteroids for assessment of altered corticoid metabolism in endocrine disease and the metabolic syndrome.

Diet1 functions in the FGF15/19 enterohepatic signaling axis to modulate bile acid and lipid levels

We identified a mutation in the Diet1 gene in a mouse strain that is resistant to hyperlipidemia and atherosclerosis. Diet1 encodes a 236 kD protein consisting of tandem low-density lipoprotein receptor and MAM (meprin-A5-protein tyrosine phosphatase mu) domains and is expressed in the enterocytes of the small intestine. Diet1-deficient mice exhibited an elevated bile acid pool size and impaired feedback regulation of hepatic Cyp7a1, which encodes the rate-limiting enzyme in bile acid synthesis. In mouse intestine and in cultured human intestinal cells, Diet1 expression levels influenced the production of fibroblast growth factor 15/19 (FGF15/19), a hormone that signals from the intestine to liver to regulate Cyp7a1. Transgenic expression of Diet1, or adenoviral-mediated Fgf15 expression, restored normal Cyp7a1 regulation in Diet-1-deficient mice. Diet1 and FGF19 proteins exhibited overlapping subcellular localization in cultured intestinal cells. These results establish Diet1 as a control point in enterohepatic bile acid signaling and lipid homeostasis.

Simultaneous and rapid analysis of bile acids including conjugates by supercritical fluid chromatography coupled to tandem mass spectrometry

A number of analysis methods for bile acids using LC-MS and GC-MS have been reported. However, there is no reported method for the simultaneous analysis of bile acids using supercritical fluid chromatography (SFC). In this study, we have successfully developed a rapid method using SFC coupled to electrospray ionization tandem mass spectrometry (ESI-MS/MS) for comprehensive bile acid profiling. 25 bile acids including glycine and taurine conjugates were analyzed simultaneously within 13min. The method was applied to rat serum samples, 24 of the bile acids were quantified without any solid-phase extraction and complicated sample preparation. This study not only reports simultaneous analysis of bile acids including conjugates but also indicates the method is applicable to a biological sample. This is the first report on the simultaneous analysis of bile acids using SFC/MS. The developed method will be an alternative to existing analysis methodology for studies on the bile acid metabolism in the medical and pharmaceutical fields.

Safety, Pharmacokinetics, and Pharmacodynamic Effects of a Selective TGR5 Agonist, SB-756050, in Type 2 Diabetes

TGR5 is a bile acid receptor and a potential target for the treatment of type 2 diabetes (T2D). We report here the safety, pharmacokinetics, and pharmacodynamic effects of a selective TGR5 agonist, SB-756050, in patients with T2D. Fifty-one subjects were randomized to receive either placebo or one of four doses of SB-756050 for 6 days. A single 100 mg dose of sitagliptin was co-administered on Day 6 to all subjects. SB-756050 was well-tolerated; it was readily absorbed, exhibited nonlinear pharmacokinetics with a less than dose-proportional increase in plasma exposure above 100 mg, and demonstrated no significant changes in exposure when co-administered with sitagliptin. SB-756050 demonstrated highly variable pharmacodynamic effects both within dose groups and between doses, with increases in glucose seen at the two lowest doses and no reduction in glucose seen at the two highest doses. The glucose effects of SB-756050 + sitagliptin were comparable to those of sitagliptin alone, even though gut hormone plasma profiles were different. This study was registered at ClinicalTrials.gov (NCT00733577).

Oral delivery of taurocholic acid linked heparin-docetaxel conjugates for cancer therapy

We have synthesized taurocholic acid (TCA) linked heparin-docetaxel (DTX) conjugates for oral delivery of anticancer drug. The ternary biomolecular conjugates formed self-assembly nanoparticles where docetaxel was located inside the core and taurocholic acid was located on the surface of the nanoparticles. The coupled taurocholic acid in the nanoparticles had enhanced oral absorption, presumably through the stimulation of a bile acid transporter of the small intestine. The oral absorption profile demonstrated that the concentration of the conjugates in plasma is about 6 fold higher than heparin alone. An anti-tumor study in MDA-MB231 and KB tumor bearing mice showed significant tumor growth inhibition activity by the ternary biomolecular conjugates. Ki-67 histology study also showed evidence of anticancer activity of the nanoparticles. Finally, noninvasive imaging using a Kodak Molecular Imaging System demonstrated that the nanoparticles were accumulated efficiently in tumors. Thus, this approach for oral delivery using taurocholic acid in the ternary biomolecular conjugates is promising for treatment of various types of cancer.