The FXR Agonist, Obeticholic Acid, Suppresses HCC Proliferation & Metastasis: Role of IL-6/STAT3 Signalling Pathway.

The nuclear receptor, farnesoid X receptor (FXR), has been recently considered as a tumor suppressor in HCC. IL-6/Janus kinase 2 (Jak-2)/signal transducer and activator of transcription 3 (STAT3) pathway has been implicated as a key player in many cancer types. This study aimed at investigating the potential effect of the FXR agonist, obeticholic acid (OCA), on HCC and the involvement of IL-6/STAT3 pathway. The potential regulation of STAT3 by its main feedback inhibitor target gene, the suppressor of cytokine signaling 3 (SOCS3), triggered by OCA was also explored. Cytotoxicity studies were performed on HepG2, Huh7, and SNU-449 cell lines using OCA alone and combined with the FXR antagonist guggulsterone (Gugg). OCA cytotoxic effect was significantly hampered in presence of Gugg. OCA also caused cell cycle arrest and inhibited invasion and migration of HCC cells. Decrease in STAT3 phosphorylation and SOCS3 upregulation were also observed. Moreover, Jak-2, IL-1ß, and IL-6 levels were decreased. These results were correlated with an upregulation of FXR and small heterodimer partner (SHP) levels. Effects of OCA on IL-6/STAT3 main key players were reversed in presence of Gugg. Overall, these findings suggest a potential effect of OCA in HCC via interfering with IL-6/STAT3 signalling pathway in vitro.

FXR mediates a chromatin looping in the GR promoter thus promoting the resolution of colitis in rodents.

Glucocorticoids (GCs) are important endocrine regulators of a wide range of physiological processes ranging from immune function to glucose and lipid metabolism. For decades, synthetic glucocorticoids such as dexamethasone have been the cornerstone for the clinical treatment of inflammatory bowel diseases (IBD). A previous study has shown that farnesoid X receptor (FXR) enhances the transcription of NR3C1 gene, which encodes for human GR, by binding to a conserved FXR response element (FXRE) in the distal promoter of this gene. In the present study we demonstrate that FXR promotes the resolution of colitis in rodents by enhancing Gr gene transcription. We used the chromatin conformation capture (3C) assay to demonstrate that this FXRE is functional in mediating a head-to-tail chromatin looping, thus increasing Gr transcription efficiency. These findings underscore the importance of FXR/GR axis in the control of intestinal inflammation.

Retinoic acid represses CYP7A1 expression in human hepatocytes and HepG2 cells by FXR/RXR-dependent and independent mechanisms.

Cholesterol 7alpha-hydroxylase (CYP7A1) plays a key role in maintaining lipid and bile salt homeostasis as it is the rate-limiting enzyme converting cholesterol to bile acids. Deficiency of CYP7A1 leads to hyperlipidemia in man and mouse. Hyperlipidemia is often seen in patients when treated with high-dose retinoic acid (RA), but the molecular mechanisms remain elusive. Our present study revealed that CYP7A1 mRNA expression is greatly repressed by RA in both human hepatocytes and HepG2 cells where increased fibroblast growth factor 19 (FGF19) and small heterodimer partner (SHP) expressions were also observed, suggesting farnesoid X receptor (FXR) and retinoid X receptor (RXR) were activated. Promoter reporter assays demonstrate that all-trans RA (atRA) specifically activated FXR/RXR. However, detailed molecular analyses indicate that this activation is through RXR, whose ligand is 9-cis RA. Knocking down of FXR or RXRalpha by small interference RNA (siRNA) in human hepatocytes increased CYP7A1 basal expression, but the repressive effect of atRA persisted, suggesting there are also FXR/RXR-independent mechanisms mediating atRA repression of CYP7A1 expression. Chromatin immunoprecipitation (ChIP) assay and cell transfection results indicate that PGC-1alpha plays a role in the FXR/RXR-independent mechanism. Our findings may provide a potential explanation for hyperlipidemic side effects observed in some patients treated with high-dose RA.

Guggulsterone antagonizes farnesoid X receptor induction of bile salt export pump but activates pregnane X receptor to inhibit cholesterol 7alpha-hydroxylase gene.

Bile acids activate a nuclear receptor, farnesoid X receptor (FXR), that induces bile salt export pump (BSEP) but inhibits cholesterol 7alpha-hydroxylase (CYP7A1) gene transcription in the liver. Guggulsterone, a plant sterol that lowers serum cholesterol, has been shown to antagonize FXR activated genes. Transient transfection assay of a human BSEP/luciferase reporter in HepG2 cells transfected with FXR reveals that guggulsterone strongly antagonizes bile acid induction of the BSEP gene. On the other hand, guggulsterone has no effect on FXR inhibition of the CYP7A1 gene, but strongly inhibits the human CYP7A1 gene by activation of pregnane X receptor (PXR). These results suggest that guggulsterone inhibits bile acid secretion from hepatocytes into bile and activates PXR to inhibit bile acid synthesis in the liver. Reduced conversion of cholesterol and bile acid excretion may lead to an increase of hepatic cholesterol and decrease of intestinal cholesterol absorption, and results in lowering serum cholesterol.

Fibrates suppress chenodeoxycholic acid-induced RANTES expression through inhibition of NF-kappaB activation.

Fibrates, hypolipidemic agents, are reported to be effective in treatment of primary biliary cirrhosis. However, the mechanism involved in therapeutic benefits of fibrates in primary biliary cirrhosis remains unknown. In contrast, hepatic regulated upon activation, normal T-cell expressed and secreted (RANTES) is increased in patients with primary biliary cirrhosis and bile acids up-regulate RANTES expression in hepatocytes. The role of fibrates in bile acid-induced RANTES expression was investigated in human hepatoma cells; 100 microM of bezafibrate and fenofibrate decreased expression of chenodeoxycholic acid-induced RANTES mRNA and protein. In addition, luciferase enzyme assay using RANTES promoter-luciferase reporter plasmid revealed that 100 microM of bezafibrate and fenofibrate transcriptionally reduced chenodeoxycholic acid-induced RANTES gene expression. Moreover, bezafibrate clearly repressed DNA-binding activity of nuclear factor-kappaB (NF-kappaB) induced by chenodeoxycholic acid. Therefore, fibrates might be inhibitory agents of inflammatory cell migration by RANTES to the liver in patients with primary biliary cirrhosis, possibly indicating that fibrates are therapeutic agents in primary biliary cirrhosis.

Characterization of chenodeoxycholic acid as an endogenous antagonist of the G-coupled formyl peptide receptors.

OBJECTIVE AND DESIGN: To demonstrate the role of bile acids in immune modulation we examined the ability of select bile acids to inhibit leukocyte migration and chemoattractant receptor function. MATERIALS: To elucidate this mechanism, we employed primary human monocytes, neutrophils and cell lines transfected to express either the high affinity fMLP receptor (FPR) or the low affinity fMLP receptor like 1 (FPRL1). TREATMENT: Cells were treated with chenodeoxycholic acid (CDCA) and related bile acids in a 0-400 micromolar range. METHOD: Cell viability, chemotaxis and calcium flux analysis were preformed. RESULTS: We observed that pathophysiological levels (< or = 150 micromolar) of CDCA competitively inhibited 3H-fMLP binding to human monocytes, FPR and FPRL1 transfected cells. Additionally, CDCA reduced both the chemotactic and calcium flux responses induced by fMLP or "W" peptide. Further, CDCA inhibited anti-FPR antibody binding to monocytes. CONCLUSIONS: CDCA selectively inhibited human leukocyte chemotaxis and calcium flux induced by fMLP, but not other chemoattractants, suggesting a mechanism for inhibition of inflammation and suppression of innate immune response.

S-adenosil-L-methionine is able to reverse the immunosuppressive effects of chenodeoxycholic acid in vitro.

The study was conceived to evaluate if S-adenosil-L-methionine, a substance commonly used in the treatment of cholestasis in patients with cirrhosis and chronic hepatitis, exerts any immunological effect and of it is able to counterbalance bile acid-mediated immunosuppression. Proliferation and interleukin 2 and interferon-gamma secretion of human lymphocytes, collected from healthy subjects and exposed to mitogenic stimuli (phytohemagglutinin, pokeweed and anti-CD3 monoclonal antibodies), were analysed in the basal condition or after exposure to S-adenosil-L-methionine and/or chenodeoxycholic acid. Chenodeoxycholic acid inhibited phytohemagglutinin-induced lymphocyte proliferation and interferon-gamma secretion, and phytohemagglutinin and pokeweed-mediated interleukin 2 secretion. S-adenosil-L-methionine did not affect lymphocyte proliferation while it reduced interleukin 2 secretion upon phytohemagglutinin and pokeweed stimulation and interferon-gamma secretion upon all stimuli tested. Moreover, S-adenosil-L-methionine counteracted chenodeoxycholic acid-mediated inhibition of lymphocyte proliferation and interleukin 2 secretion. The results of our study confirm the immunosuppressive role of chenodeoxycholic acid on both secretive and proliferative lymphocyte functions and provide evidence of immunomodulatory activities of S-adenosil-L-methionine and its capacity to antagonize chenodeoxycholic acid-mediated inhibition of lymphocyte proliferation and interleukin 2 secretion.

Cyclosporin A blocks bile acid synthesis in cultured hepatocytes by specific inhibition of chenodeoxycholic acid synthesis.

Bile acid synthesis, determined by conversion of [4-14C]cholesterol into bile acids in rat and human hepatocytes and by measurement of mass production of bile acids in rat hepatocytes, was dose-dependently decreased by cyclosporin A, with 52% (rat) and 45% (human) inhibition of 10 microM. The decreased bile acid production in rat hepatocytes was due only to a fall in the synthesis of beta-muricholic and chenodeoxycholic acids (-64% at 10 microM-cyclosporin A), with no change in the formation of cholic acid. In isolated rat liver mitochondria, 26-hydroxylation of cholesterol was potently inhibited by the drug (concn. giving half-maximal inhibition = 4 microM). These results suggest that cyclosporin A blocks the alternative pathway in bile acid synthesis, which leads preferentially to the formation of chenodeoxycholic acid.

Protective effect of tauroursodeoxycholate against chenodeoxycholate-induced damage to cultured rabbit gastric cells.

Ursodeoxycholate (UDC) and tauroursodeoxycholate (TUDC) have been reported to be protective against liver injury induced by other bile salts. UDC also has been shown to be effective against refluxed bile-induced gastritis after gastric surgery. However the mechanism of the therapeutic effect of UDC on gastric mucosa has not been known. In the present study, cytoprotective actions of UDC and TUDC against chenodeoxycholate (CDC)-induced gastric injury were investigated using rabbit gastric cell cultures without systemic factors. Rabbit gastric mucosal cells were cultured after the isolation of rabbit gastric cells with collagenase and ethylenediaminetetraacetic acid. Cytotoxicity was quantified by measuring 51Cr release from prelabeled cells and MTT assay. Prostaglandin (PG) E2 was assayed by radioimmunoassay. Concentrations of CDC greater than 0.5 mM or UDC greater than 5 mM caused cellular damage and increased 51Cr release in a dose-dependent and time-dependent fashion, while TUDC up to 10 mM did not. TUDC, but not UDC, showed a significant decrease of CDC (1.5 mM)-induced 51Cr release dose dependently. The protective effect of TUDC against CDC-induced damage was confirmed by MTT assay. On phase-contrast microscopy, disruption of monolayers induced by CDC (1.5 mM) was clearly protected by TUDC (10 mM). Free radical scavengers (500 units/ml of superoxide dismutase, 300 units/ml of catalase, and 100 mM of dimethyl sulfoxide) or a calcium blocker (10(-7)-10(-5) M verapamil) did not show significant protection against CDC-induced damage. Deprivation of Ca2+ in the media did not affect CDC-induced damage. Thus free radicals or Ca2+ might not be involved in the cell toxicity of CDC.(ABSTRACT TRUNCATED AT 250 WORDS)

16,16-Dimethyl prostaglandin E2 induces villus contraction in rats without affecting intestinal restitution.

In a previous study we found that 16,16-dimethyl prostaglandin E2 protects the small intestine against chenodeoxycholic acid injury in the rat. One possible explanation for prostaglandin's protective action may be that prostaglandin-induced villus contraction accelerates mucosal restitution. This hypothesis was tested in rats by perfusing intestinal segments in vivo in a single-pass fashion with 0.125-0.5 micrograms/L of 16,16-dimethyl prostaglandin E2. These studies showed a dose-dependent, reversible contraction of intestinal villi and crypts. To test the effect of this contraction on mucosal restitution, standardized intestinal injury was produced in indomethacin-pretreated rats perfused in vivo with 5 mmol/L chenodeoxycholic acid. The rats were then perfused with bile acid-free buffer containing either 0.5 microgram/mL of 16,16-dimethyl prostaglandin E2 or vehicle. This study showed that despite decreasing villus height after bile acid injury, 16,16-dimethyl prostaglandin E2 did not significantly affect the rate of morphologic (assessed by villus denudation) or functional (assessed by mannitol and water absorption) restitution of the injured intestinal mucosa. Thus, although 16,16-dimethyl prostaglandin E2 causes villus contraction, this effect does not result in more rapid restitution of the injured intestinal mucosa and is not a likely mechanism for prostaglandin-mediated protection of the intestinal mucosa.

Colon cancer and dietary fiber: cellulose inhibits the DNA-damaging ability of bile acids.

Colon cancer is the second most common type of cancer in the United States. Bile acids have been implicated in the etiology of this disease. In a previous study, we showed that bile acids can damage DNA in vitro. In this study, we report that this damage is largely prevented when the bile acids are pretreated with cellulose fiber. Preliminary data show that cellulose may act as a catalyst to promote polyesterification of bile acid to a biologically inactive form.

Effect of 16,16-dimethyl PGE2 and indomethacin on bile acid-induced intestinal injury and restitution in rats.

Topically administered 16,16-dimethyl prostaglandin E2 reduced bile acid-induced small intestinal mucosal injury; however, the time course of restitution after such injury and whether either exogenous or endogenous prostaglandins affect this restitution are unknown. To explore these questions, mucosal injury was produced in 50 cm small intestinal segments of anesthetized male Sprague-Dawley rats perfused in vivo for 0, 5, 15, 30, or 45 minutes with buffer containing 5 mmol/L chenodeoxycholic acid, and to assess mucosal restitution, additional rats were perfused for 45 minutes with chenodeoxycholic acid followed by 15, 30, 60 or 120 minutes with chenodeoxycholate-free buffer. The above studies were then repeated in rats receiving either intraperitoneal indomethacin (10 mg/kg) or 15 minutes of preperfusion with buffer containing 1.4 mumol/L (0.5 microgram/ml) 16,16-dimethyl prostaglandin E2. Prostaglandin pretreatment reduced and indomethacin pretreatment increased significantly the morphologic (as measured by quantitative histology) and functional (as measured by mannitol and water absorption) mucosal injury caused by chenodeoxycholic acid. However, neither pretreatment had a major impact on the time course of functional or morphologic mucosal restitution, with nearly complete restitution occurring within 1 hour. Thus, although both endogenous and exogenous prostaglandins have a significant impact on bile acid-induced small intestinal mucosal injury, this effect is not caused by an acceleration of the rate of mucosal restitution.

Chenodeoxycholic acid-induced diarrhea in rats: effects of atropine and codeine.

Orally administered chenodeoxycholic acid (300 mg/kg) produced diarrhea and accumulation of gastro-intestinal fluid in rats. The fluid in the stomach and small intestine remained accumulated even after the accumulated colonic fluid and the diarrheal excretion decreased. When instilled into an intestinal closed-loop, chenodeoxycholic acid caused a marked inhibition of fluid absorption in the colon and jejunum but less effect in the ileum. On the contrary, an intravenous administration of chenodeoxycholic acid caused neither diarrhea nor impairment of colonic absorption of fluid. Atropine and codeine (10 mg/kg s.c.) blocked or at least delayed the diarrhea produced by oral administration of chenodeoxycholic acid. The antidiarrheal activity of codeine was found to be more potent and longer-lasting than that of atropine. Both drugs delayed the passage of chenodeoxycholic acid containing gastric fluid into the duodenum, but neither of them prevented chenodeoxycholic acid-induced jejunal secretion of fluid and electrolytes. These results indicate that the diarrheal excretion by chenodeoxycholic acid was ascribable to the impairment of fluid absorption in the colonic mucosa and partly to the activation of gastro-intestinal propulsive motility.

Dietary cholesterol affects chenodeoxycholic acid action on biliary lipids.

Chenodeoxycholic acid (CDC) decreases biliary saturation and dissolves gallstones in one-half of the treated patients. Dietary cholesterol also affects biliary lipids and is a possible factor explaining unsuccessful CDC therapy. The aim of this investigation was to study the effect of high and low dietary cholesterol on the CDC-induced decrease of biliary saturation and activity of hepatic hydroxymethylglutaryl coenzyme A reductase (HMG-CoAR). Seventy two hamsters in six groups were fed for 1 month one of three diets: 0.8 mg of cholesterol per g of food, 2.4 mg of cholesterol per g, or cholesterol-free. On each diet hamsters received no CDC or CDC 30 mg per kg per day. When animals were killed, biliary lipids were determined and the activity of hepatic HMG-CoAR was assayed. CDC administration decreased the saturation index (SI)(P less than 0.01) in hamsters on the high cholesterol and standard diets but not on the cholesterol-free diet. The SI in CDC-treated hamsters on the high cholesterol (0.78 +/- 0.03) and cholesterol-free (0.68 +/- 0.02) diets were greater (P less than 0.02) than in CDC-treated hamsters on the standard diet (0.48 +/- 0.03). CDC decreased (P less than 0.01) HMG-CoA reductase activity on each diet. In comparison to HMG-CoAR activity (190 +/- 7.6 pmoles per mg per min) in CDC-treated hamsters on the standard diet, the activity in CDC-treated hamsters on the high cholesterol diet (176 +/- 5.8 pmoles per mg per min) was decreased ( less than 0.05), whereas the activity on the cholesterol-free diet (495 +/- 11.5 pmoles per mg per min) was greater (P less than 0.01). It is concluded that: (1) dietary cholesterol is necessary for optimum CDC inhibition of HMG-CoAR; (2) high cholesterol and cholesterol-free diets prevent maximum CDC decrease of the biliary saturation index; (3) dietary cholesterol alterations may therefore be one cause of the failure of CDC dissolution of gallstones.

Effect of conjugated dihydroxy bile salts on electrolyte transport in rat colon.

The mechanism by which excess quantities of bile salts in the colon produce diarrhea is not known. Therefore, experiments were performed in which the effect of conjugated dihydroxy bile salts on ion transport was evaluated in the in vitro short-circuited rat colon. 2 mM glycochenodeoxycholic acid (GCDC), taurochenodeoxycholic acid (TCDC), or taurodeoxycholic acid caused a prompt increase in short-circuit current (I(sc)) and electrical potential difference (PD). Similar results were obtained when theophylline was added. Removal of HCO(2) and C1 prevented the effects of both bile salts and theophylline. Pretreatment with theophylline blocked the increase in I(sc) and PD produced by TCDC and pretreatment with either TCDC or GCDC inhibited the expected theophylline response. Na fluxes in the presence of both TCDC and theophylline demonstrated a decrease in net absorption; and TCDC decreased net C1 absorption and theophylline caused a reversal of net C1 absorption to net C1 secretion. It is proposed that the diarrhea associated with cholerheic enteropathy is produced by active anion secretion possibly mediated by cyclic AMP.