Vitamin D3 modulates the expression of bile acid regulatory genes and represses inflammation in bile duct-ligated mice

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Protein-centric omics analysis reveals circulating complements linked to non-viral liver diseases as potential therapeutic targets

BACKGROUND/AIMS

To evaluate the causal correlation between complement components and non-viral liver diseases and their potential use as druggable targets.

METHODS

We conducted Mendelian randomization (MR) to assess the causal role of circulating complements in the risk of non-viral liver diseases. A complement-centric protein interaction network was constructed to explore biological functions and identify potential therapeutic options.

RESULTS

In the MR analysis, genetically predicted levels of complement C1q C chain (C1QC) were positively associated with the risk of autoimmune hepatitis (odds ratio 1.125, 95% confidence interval 1.018-1.244), while complement factor H-related protein 5 (CFHR5) was positively associated with the risk of primary sclerosing cholangitis (PSC;1.193, 1.048- 1.357). On the other hand, CFHR1 (0.621, 0.497-0.776) and CFHR2 (0.824, 0.703-0.965) were inversely associated with the risk of alcohol-related cirrhosis. There were also significant inverse associations between C8 gamma chain (C8G) and PSC (0.832, 0.707-0.979), as well as the risk of metabolic dysfunction-associated steatotic liver disease (1.167, 1.036-1.314). Additionally, C1S (0.111, 0.018-0.672), C7 (1.631, 1.190-2.236), and CFHR2 (1.279, 1.059-1.546) were significantly associated with the risk of hepatocellular carcinoma. Proteins from the complement regulatory networks and various liver diseaserelated proteins share common biological processes. Furthermore, potential therapeutic drugs for various liver diseases were identified through drug repurposing based on the complement regulatory network.

CONCLUSION

Our study suggests that certain complement components, including C1S, C1QC, CFHR1, CFHR2, CFHR5, C7, and C8G, might play a role in non-viral liver diseases and could be potential targets for drug development.

Vitamin D Receptor Mediates Attenuating Effect of Lithocholic Acid on Dextran Sulfate Sodium Induced Colitis in Mice

Bile acids are major components of bile; they emulsify dietary lipids for efficient digestion and absorption and act as signaling molecules that activate nuclear and membrane receptors. The vitamin D receptor (VDR) is a receptor for the active form of vitamin D and lithocholic acid (LCA), a secondary bile acid produced by the intestinal microflora. Unlike other bile acids that enter the enterohepatic circulation, LCA is poorly absorbed in the intestine. Although vitamin D signaling regulates various physiological functions, including calcium metabolism and inflammation/immunity, LCA signaling remains largely unknown. In this study, we investigated the effect of the oral administration of LCA on colitis in a mouse model using dextran sulfate sodium (DSS). Oral LCA decreased the disease activity of colitis in the early phase, which is a phenotype associated with the suppression of histological injury, such as inflammatory cell infiltration and goblet cell loss. These protective effects of LCA were abolished in VDR-deleted mice. LCA decreased the expression of inflammatory cytokine genes, but this effect was at least partly observed in VDR-deleted mice. The pharmacological effect of LCA on colitis was not associated with hypercalcemia, an adverse effect induced by vitamin D compounds. Therefore, LCA suppresses DSS-induced intestinal injury in its action as a VDR ligand.

Cumulative Erythemal Ultraviolet Radiation and Risk of Cancer in 3 Large US Prospective Cohorts

Ultraviolet radiation (UVR) exposure is the major risk factor for melanoma. However, epidemiologic studies on UVR and noncutaneous cancers have reported inconsistent results, with some suggesting an inverse relationship potentially mediated by vitamin D. To address this, we examined 3 US prospective cohorts, the Health Professionals Follow-up Study (HPFS) (1986) and Nurses' Health Study (NHS) I and II (1976 and 1989), for associations between cumulative erythemal UVR and incident cancer risk, excluding nonmelanoma skin cancer. We used a validated spatiotemporal model to calculate erythemal UVR. Participants (47,714 men; 212,449 women) were stratified into quintiles by cumulative average erythemal UVR, using the first quintile as referent, for Cox proportional hazards regression analysis. In the multivariable-adjusted meta-analysis of all cohorts, compared with the lowest quintile, risk of any cancer was slightly increased across all other quintiles (highest quintile hazard ratio (HR) = 1.04, 95% confidence interval (CI): 1.01, 1.07; P for heterogeneity = 0.41). All UVR quintiles were associated with similarly increased risk of any cancer excluding melanoma. As expected, erythemal UVR was positively associated with risk of melanoma (highest quintile HR = 1.17, 95% CI: 1.04, 1.31; P for heterogeneity = 0.83). These findings suggest that elevated UVR is associated with increased risk of both melanoma and noncutaneous cancers.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Vitamin D receptor upregulates tight junction protein claudin-5 against colitis-associated tumorigenesis

Tight junctions are essential for barrier integrity, inflammation, and cancer. Vitamin D and the vitamin D receptor (VDR) play important roles in colorectal cancer (CRC). Using the human CRC database, we found colonic VDR expression was low and significantly correlated with a reduction of Claudin-5 mRNA and protein. In the colon of VDR^ΔIEC mice, deletion of intestinal VDR led to lower protein and mRNA levels of Claudin-5. Intestinal permeability was increased in the VDR^-/- colon cancer model. Lacking VDR and a reduction of Claudin-5 are associated with an increased number of tumors in the VDR^-/- and VDR^ΔIEC mice. Furthermore, gain and loss functional studies have identified CLDN-5 as a downstream target of VDR. We identified the Vitamin D response element (VDRE) binding sites in a reporter system showed that VDRE in the Claudin-5 promoter is required for vitamin D₃-induced Claudin-5 expression. Conditional epithelial VDR overexpression protected against the loss of Claudin-5 in response to inflammation and tumorigenesis in vivo. We also reported fecal VDR reduction in a colon cancer model. This study advances the understanding of how VDR regulates intestinal barrier functions in tumorigenesis and the possibility for identifying new biomarker and therapeutic targets to restore VDR-dependent functions in CRC.

Vitamin D Receptor Influences Intestinal Barriers in Health and Disease

Vitamin D receptor (VDR) executes most of the biological functions of vitamin D. Beyond this, VDR is a transcriptional factor regulating the expression levels of many target genes, such as genes for tight junction proteins claudin-2, -5, -12, and -15. In this review, we discuss the progress of research on VDR that influences intestinal barriers in health and disease. We searched PubMed and Google Scholar using key words vitamin D, VDR, tight junctions, cancer, inflammation, and infection. We summarize the literature and progress reports on VDR regulation of tight junction distribution, cellular functions, and mechanisms (directly or indirectly). We review the impacts of VDR on barriers in various diseases, e.g., colon cancer, infection, inflammatory bowel disease, and chronic inflammatory lung diseases. We also discuss the limits of current studies and future directions. Deeper understanding of the mechanisms by which the VDR signaling regulates intestinal barrier functions allow us to develop efficient and effective therapeutic strategies based on levels of tight junction proteins and vitamin D/VDR statuses for human diseases.

Vitamin D Deficiency Impacts Exposure and Response of Pravastatin in Male Rats by Altering Hepatic OATPs

This study aimed to determine the effect of vitamin D (VD) deficiency on the efficacy and pharmacokinetics of pravastatin and clarify whether the effects are mediated by Organic anion-transporting polypeptides (OATPs). Experiments were conducted in rats to explore the effect of VD deficiency on the pharmacodynamics and pharmacokinetics of pravastatin. In the pharmacodynamic study, rats were fed a VD-free or VD-supplement high-fat diet for 25–30 days, and plasma 25(OH)VD was dynamically monitored. The response of pravastatin (changes in blood lipids) on rats were then examined after 15 days of pravastatin treatment. In the pharmacokinetic study, rats were fed a VD-free or VD-supplement diet for 25–30 days. The pharmacokinetics of single oral dose pravastatin was then studied, and intestinal and hepatic Oatp1a1 and Oatp2b1 expression was determined using quantitative polymerase chain reaction (qPCR) and western blot. Furthermore, OATP1B1 and OATP2B1 expression in Huh7 cells with or without 1.25(OH)₂D were assessed via qPCR and western blot. For the pharmacodynamic study, the decrease of total cholesterol and increase of high-density lipoprotein cholesterol in VD-deficient rats were smaller than in VD-sufficient rats, indicating that VD deficiency reduced the response of pravastatin in rats. For the pharmacokinetic study, the plasma exposure slightly increased, and liver exposure decreased in VD-deficient rats, but not significantly. VD deficiency decreased the Oatp1a1 and Oatp2b1 expression in the liver, but not in the small intestine. Similarly, OATP1B1 and OATP2B1 protein levels in Huh7 cells were reduced when 1.25(OH)₂D was absent. In conclusion, VD deficiency can decrease the response of pravastatin in rats by reducing the liver pravastatin exposure and expression of hepatic OATPs, consistent with the extended hepatic clearance model theory.

Oral benzo[a]pyrene administration attenuates dextran sulfate sodium-induced colitis in mice

Benzo[a]pyrene (BaP) is an environmental pollutant produced by combustion processes and is present in grilled foods as well as in tobacco smoke. BaP acts as an agonist for the aryl hydrocarbon receptor (AHR), and is metabolized by AHR-inducing enzymes. BaP metabolism can result in either detoxification or metabolic activation, the latter leads to an increased risk of disease, particularly lung cancer and cardiovascular disease, in a context-dependent manner. Although AHR activation has been thought to protect against inflammatory bowel disease, it remains unknown whether BaP exerts a protective or deleterious effect on colitis. In this study, we examined the effect of oral BaP administration on colitis induced by dextran sulfate sodium (DSS) in mice, an animal model of inflammatory bowel disease. BaP administration attenuated weight loss, shortening of the colon, disease activity index scores, and histological damage in DSS-induced colitis mice. BaP also suppressed colonic expression of inflammation-associated genes and plasma interleukin-6 secretion induced by DSS treatment. BaP-DNA adduct formation, a marker of BaP metabolic activation, was not enhanced in the colon after DSS treatment. Thus, oral BaP exerts an anti-inflammatory effect on DSS-induced colitis, without the toxicity associated with metabolic activation. The results provide insights into the disease-specific roles of BaP.

Liver X receptors regulate natural killer T cell population and antitumor activity in the liver of mice

The nuclear receptors liver X receptor α (LXRα) and LXRβ are lipid sensors that regulate lipid metabolism and immunity. Natural killer T (NKT) cells, a T cell subset expressing surface markers of both natural killer cells and T lymphocytes and involved in antitumor immunity, are another abundant immune cell type in the liver. The potential function of the metabolic regulators LXRα/β in hepatic NKT cells remains unknown. In this study, we examined the role of LXRα and LXRβ in NKT cells using mice deficient for LXRα and/or LXRβ, and found that hepatic invariant NKT (iNKT) cells are drastically decreased in LXRα/β-KO mice. Cytokine production stimulated by the iNKT cell activator α-galactosylceramide was impaired in LXRα/β-KO hepatic mononuclear cells and in LXRα/β-KO mice. iNKT cell-mediated antitumor effect was also disturbed in LXRα/β-KO mice. LXRα/β-KO mice transplanted with wild-type bone marrow showed decreased iNKT cells in the liver and spleen. The thymus of LXRα/β-KO mice showed a decreased population of iNKT cells. In conclusion, LXRα and LXRβ are essential for NKT cell-mediated immunity, such as cytokine production and hepatic antitumor activity, and are involved in NKT cell development in immune tissues, such as the thymus.

Yes-associated protein regulates the hepatoprotective effect of vitamin D receptor activation through promoting adaptive bile duct remodeling in cholestatic mice

Mounting clinical evidence has revealed that the vitamin D receptor (VDR) is associated with cholestatic liver injury, although the functions of VDR in this condition remain largely unexplored. Here, we investigated the effects of VDR activation on bile duct ligation (BDL) mice, and the underlying mechanisms were further investigated. A low-calcemic VDR agonist, paricalcitol (PAL, 200 ng/kg), was intraperitoneally injected into BDL mice every other day for 5 days or 28 days. Liver histology, liver function indicators, cholangiocyte proliferation, fibrosis scores, and inflammation were evaluated. Mice treated with PAL were rescued from the decreased survival rate induced by BDL and liver damage was reduced. Mechanistically, PAL promoted cholangiocyte proliferation, which was likely conducive to proliferating bile duct maturation and increased branching of bile ducts. PAL treatment also increased the expression of Yes-associated protein (YAP) and its target protein epithelial cell adhesion molecule (EpCam) and decreased the level of inactive cytoplasmic phosphorylated YAP. YAP knockdown abrogated PAL-induced primary bile duct epithelial cell proliferation, confirmed with YAP inhibitor administration. In addition, BDL-induced liver fibrosis and inflammatory cell infiltration were reduced by PAL treatment at both day 5 and day 28 post-BDL. In conclusion, VDR activation mitigates cholestatic liver injury by promoting adaptive bile duct remodeling through cholangiocytic YAP upregulation. Because PAL is an approved clinical drug, it may be useful for treatment of cholestatic liver disease. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Vitamin D receptor is overexpressed in the duodenum of patients with irritable bowel syndrome

BACKGROUND AND AIM

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders, and bile acids are thought to be associated with the pathogenesis of IBS. Bile acid receptors are expressed on intestinal epithelial cells. However, no study has assessed bile acid receptor proteins in IBS. Therefore, we examined the intestinal mucosal expression of bile acid receptors in patients with IBS.

METHODS

Intestinal biopsies were performed in patients with IBS and controls. Mast cells, vitamin D receptor (VDR), and somatostatin were stained with specific antibodies. Levels of VDR, farnesoid X receptor (FXR), takeda-G-protein-receptor-5 (TGR5), claudins, and transient-receptor-potential-cation-channel-subfamily-V-member 6 (TRPV6) were assessed by western blotting.

RESULTS

3Mast cell counts in the second part of the duodenum were significantly higher in patients with IBS than in controls. VDR protein levels were significantly elevated in the duodenum and terminal ileum of patients with IBS compared with controls, although this difference was not seen in the cecum or rectum. FXR and TGR5 protein levels did not differ in any part of the intestine. VDR-positive cryptal epithelia in IBS were distributed not only at basal crypt but also along the upper part of the basal crypt epithelial cells. In contrast, the pattern of gut somatostatin-positive cells, claudins, and TRPV6 levels did not differ.

CONCLUSIONS

The number of mast cells in the duodenum was significantly increased, and the protein expression levels of VDR, but not those of FXR or TGR5, were elevated in the duodenal epithelial crypt in patients with IBS.

Enzyme-treated soy protein supplementation in low protein diet enhanced immune function of immune organs in on-growing grass carp

A 56 days feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on immune function of immune organs (head kidney, spleen and skin) in on-growing grass carp. A total of 540 on-growing grass carp (initial average weight: 325.72 ± 0.60 g) were fed six diets, which included a normal protein diet (28% crude protein) and five low protein diets (26% crude protein) supplemented with graded levels of ETSP (0.0, 0.8, 1.2, 1.6 and 2.0%). At the end of feeding period, a challenge test was performed by infection with Aeromonas hydrophila for two weeks. The results indicated that (1) reducing dietary protein content from 28 to 26% decreased antibacterial substances and aggravated inflammatory responses of above three immune organs; (2) under the condition of reducing protein level in diet, 0.8-1.2% ETSP supplementation reversed these above adverse effects on immune function of above three immune organs; (3) suitable ETSP supplementation-decreased inflammatory responses were partly associated with [IκB kinase β (IKKβ)/inhibitor of κBα (IκBα)/nuclear factor kappa B (NF-κB) p65 and p52 or NF-κB p65] signaling and [target of rapamycin (TOR)/(S6K1, 4E-BP)] signaling in above three immune organs. (4) On the basis of C3 content (head kidney), C4 content (spleen) and skin hemorrhage and lesion, the optimal ETSP supplementation levels in low protein diets were estimated to be 1.48%, 1.61% and 1.03%, respectively. In summary, ETSP supplementation in low protein diets improved immune function of head kidney, spleen and skin in on-growing grass carp.

Vitamin D Receptor Deletion Changes Bile Acid Composition in Mice Orally Administered Chenodeoxycholic Acid

The vitamin D receptor (VDR) is a nuclear receptor for the active form of vitamin D₃ and also for the secondary bile acid lithocholic acid (LCA). The in vivo role of VDR in bile acid metabolism remains largely uncharacterized. We previously reported that pharmacological VDR activation enhances urinary bile acid excretion, particularly in mice fed chow supplemented with chenodeoxycholic acid (CDCA), which is metabolized to muricholic acid in mouse liver and is also converted to LCA by intestinal bacteria. In this study, we examined the effect of VDR deletion on bile acid composition utilizing VDR-knockout (VDR-KO) mice. VDR deletion did not change total bile acid levels in liver or feces of mice when fed standard chow supplemented with calcium, needed to prevent hypocalcemia in VDR-KO mice. Total bile acid levels in plasma and urine tended to be higher and lower, respectively, in VDR-KO mice. After feeding CDCA-supplemented chow, VDR-KO mice showed decreased hepatic, fecal and urinary total bile acid and CDCA levels compared to wild-type mice. Plasma total bile acids and LCA were relatively high in these mice. These results indicate that VDR deletion influences CDCA metabolism. VDR may play a role in the excretion of excess bile acids.

Lactic Acid Bacteria Isolated From Korean Kimchi Activate the Vitamin D Receptor-autophagy Signaling Pathways

BACKGROUND

Probiotic lactic acid bacteria (LAB) have been used in the anti-inflammation and anti-infection process of various diseases, including inflammatory bowel disease (IBD). Vitamin D receptor (VDR) plays an essential role in pathogenesis of IBD and infectious diseases. Previous studies have demonstrated that the human VDR gene is a key host factor to shape gut microbiome. Furthermore, intestinal epithelial VDR conditional knockout (VDRΔIEC) leads to dysbiosis. Low expressions of VDR is associated with impaired autophagy, accompanied by a reduction of ATG16L1 and LC3B. The purpose of this study is to investigate probiotic effects and mechanism in modulating the VDR-autophagy pathways.

METHODS

Five LAB strains were isolated from Korean kimchi. Conditional medium (CM) from these strains was used to treat a human cell line HCT116 or intestinal organoids to measure the expression of VDR and autophagy. Mouse embryonic fibroblast (MEF) cells with or without VDR were used to investigate the dependence on the VDR signaling. To test the role of LAB in anti-inflammation, VDR+/+ organoids were treated with 121-CM before infection with Salmonella enterica serovar Enteritidis. In vivo, the role of LAB in regulating VDR-autophagy signaling was examined using LAB 121-CM orally administrated to VDRLoxp and VDRΔIEC mice.

RESULTS

The LAB-CM-treated groups showed higher mRNA expression of VDR and its target genes cathelicidin compared with the control group. LAB treatment also enhanced expressions of Beclin-1 and ATG16L1 and changed the ratio of LC3B I and II, indicating the activation of autophagic responses. Furthermore, 121-CM treatment before Salmonella enterica serovar Enteritidis infection dramatically increased VDR and ATG16L1 and inhibited the inflammation. Administration of 121-CM to VDRLoxp and VDRΔIEC mice for 12 and 24 hours resulted in an increase of VDR and LC3B II:I ratio. Furthermore, we identified that probiotic proteins P40 and P75 in the LAB-CM contributed to the anti-inflammatory function by increasing VDR.

CONCLUSIONS

Probiotic LAB exert anti-inflammation activity and induces autophagy. These effects depend on the VDR expression. Our data highlight the beneficial effects of these 5 LAB strains isolated from food in anti-infection and anti-inflammation.

Fermentable fibers induce rapid macro- and micronutrient depletion in Toll-like receptor 5-deficient mice

Functional fermentable fibers are considered essential for a healthy diet. Recently, we demonstrated that gut microbiota dysbiotic mice fed an inulin-containing diet (ICD) developed hepatocellular carcinoma (HCC) within 6 mo. In particular, a subset of Toll-like receptor 5-deficient (T5KO) mice prone to HCC exhibited rapid onset of hyperbilirubinemia (HB) and cholemia; these symptoms provide rationale that ICD induces cholestasis. Our objective in the present study was to determine whether inulin-fed T5KO-HB mice exhibit other known consequences of cholestasis, including essential fatty acid and fat-soluble vitamin deficiencies. Here, we measured hepatic fatty acids and serum vitamin A and D levels from wild-type (WT), T5KO low bilirubin (LB) and T5KO-HB mice fed ICD for 4 wk. Additionally, hepatic RNAseq and proteomics were performed to ascertain other metabolic alterations. Compared with WT and T5KO-LB, T5KO-HB mice exhibited steatorrhea, i.e., ~50% increase in fecal lipids. This could contribute to the significant reduction of linoleate in hepatic neutral lipids in T5KO-HB mice. Additionally, serum vitamins A and D were ~50% reduced in T5KO-HB mice, which was associated with metabolic compromises. Overall, our study highlights that fermentable fiber-induced cholestasis is further characterized by depletion of macro-and micronutrients.NEW & NOTEWORTHY Feeding a dietary, fermentable fiber diet to a subset of Toll-like receptor 5 deficient (T5KO) mice induces early onset hyperbilirubinemia and cholemia that later manifests to hepatocellular carcinoma (HCC). Our study highlights that fermentable fiber-induced cholestasis is characterized with modest macro- and micronutrient deficiencies that may further contribute to hepatic biliary disease. Compared with chemical induction, immunization, surgery, or genetic manipulation, these findings provide a novel approach to study the cholestatic subtype of HCC.

Calcipotriol Inhibits NLRP3 Signal Through YAP1 Activation to Alleviate Cholestatic Liver Injury and Fibrosis

Cholestasis is common in multiple clinical circumstances. The NOD-like receptor protein 3 (NLRP3) inflammasome pathway has been demonstrated to play an important role in liver injury and fibrosis induced by cholestasis. We previously proved that MCC950, a selective NLRP3 inhibitor, alleviates liver fibrosis and injury in experimental liver cholestasis induced by bile-duct ligation (BDL) in mice. Herein, we investigate the role of calcipotriol, a potent vitamin D receptor agonist, in experimental liver cholestasis, test its therapeutic efficacy, and explore its potential protective mechanism. C57BL/6 mice were made to undergo BDL or fed the 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet to establish two classic cholestatic models. Calcipotriol was administered intraperitoneally to these mice daily. Serum makers of liver damage and integrity, liver histological changes, levels of liver pro-fibrotic markers, bile acid synthetases and transporters were measured in vivo. The underlying mechanism by which calcipotriol alleviates cholestatic liver injury and fibrosis was further investigated. The results of the current study demonstrated that calcipotriol supplement significantly alleviate cholestatic liver injury and fibrosis. Moreover, calcipotriol supplement markedly inhibited NLRP3 inflammasome pathway activation to alleviate liver injury and fibrosis in vivo and inhibit hepatic stellate cell (HSC) activation in vitro. In addition, VDR agonist calcipotriol exert inhibitory effect on NLRP3 inflammasome activation through activating yes-associated protein 1 (YAP1). In conclusion, our findings proved that calcipotriol suppressed the NLRP3 signal by activating YAP1 to alleviate liver injury and retard fibrogenesis in cholestasis.

Pathophysiological Role and Therapeutic Implications of Vitamin D in Autoimmunity: Focus on Chronic Autoimmune Diseases

Vitamin D is a pleiotropic secosteroid yielding multiple actions in human physiology. Besides the canonical regulatory activity on bone metabolism, several non-classical actions have been described and the ability of vitamin D to partake in the regulation of the immune system is particularly interesting, though far stronger and convincing evidence has been collected in in vitro as compared to in vivo studies. Whether vitamin D is able to regulate at physiological concentrations the human immune system remains unproven to date. Consequently, it is not established if vitamin D status is a factor involved in the pathogenesis of immune-mediated diseases and if cholecalciferol supplementation acts as an adjuvant for autoimmune diseases. The development of autoimmunity is a heterogeneous process, which may involve different organs and systems with a wide range of clinical implications. In the present paper, we reviewed the current evidences regarding vitamin D role in the pathogenesis and management of different autoimmune diseases.

Effects of vitamin D on drugs: Response and disposal

Vitamin D supplementation and vitamin D deficiency are common in clinical experience and in daily life. Vitamin D not only promotes calcium absorption and immune regulation, but also changes drug effects (pharmacodynamics and adverse reactions) and drug disposal in vivo when combined with various commonly used clinical drugs. The extensive physiological effects of vitamin D may cause synergism effects or alleviation of adverse reactions, and vitamin D's affect on drugs in vivo disposal through drug transporters or metabolic enzymes may also lead to changes in drug effects. Herein, the effects of vitamin D combined with commonly used drugs were reviewed from the perspective of drug efficacy and adverse reactions. The effects of vitamin D on drug transport and metabolism were summarized and analyzed. Hopefully, more attention will be paid to vitamin D supplementation and deficiency in clinical treatment and drug research and development.

The challenges of primary biliary cholangitis: What is new and what needs to be done

Primary Biliary Cholangitis (PBC) is an uncommon, chronic, cholangiopathy of autoimmune origin and unknown etiology characterized by positive anti-mitochondrial autoantibodies (AMA), female preponderance and progression to cirrhosis if left untreated. The diagnosis is based on AMA- or PBC-specific anti-nuclear antibody (ANA)-positivity in the presence of a cholestatic biochemical profile, histologic confirmation being mandatory only in seronegative cases. First-line treatment is ursodeoxycholic acid (UDCA), which is effective in preventing disease progression in about two thirds of the patients. The only approved second-line treatment is obeticholic acid. This article summarizes the most relevant conclusions of a meeting held in Lugano, Switzerland, from September 23rd-25th 2018, gathering basic and clinical scientists with various background from around the world to discuss the latest advances in PBC research. The meeting was dedicated to Ian Mackay, pioneer in the field of autoimmune liver diseases. The role of liver histology needs to be reconsidered: liver pathology consistent with PBC in AMA-positive individuals without biochemical cholestasis is increasingly reported, raising the question as to whether biochemical cholestasis is a reliable disease marker for both clinical practice and trials. The urgent need for new biomarkers, including more accurate markers of cholestasis, was also widely discussed during the meeting. Moreover, new insights in interactions of bile acids with biliary epithelia in PBC provide solid evidence of a role for impaired epithelial protection against potentially toxic hydrophobic bile acids, raising the fundamental question as to whether this bile acid-induced epithelial damage is the cause or the consequence of the autoimmune attack to the biliary epithelium. Strategies are needed to identify difficult-to-treat patients at an early disease stage, when new therapeutic approaches targeting immunologic pathways, in addition to bile acid-based therapies, may be effective. In conclusion, using interdisciplinary approaches, groundbreaking advances can be expected before long in respect to our understanding of the etiopathogenesis of PBC, with the ultimate aim of improving its treatment.

Frontline Science: Concanavalin A-induced acute hepatitis is attenuated in vitamin D receptor knockout mice with decreased immune cell function

The vitamin D receptor (VDR) is a nuclear receptor for the active form of vitamin D, 1α,25-dihydroxyvitamin D₃ , and regulates various physiologic processes, such as bone and calcium metabolism, cellular proliferation and differentiation, and immunity. VDR is highly expressed in the intestine, kidney, bone, and macrophages, but is expressed at a low level in the liver. The liver is a major metabolic organ and also acts as an immune gateway for dietary nutrients and xenobiotics. In this study, we investigated the function of VDR in hepatic immune cells, such as Kupffer cells/macrophages, utilizing VDR knockout (KO) mice. We showed that VDR is functionally expressed in hepatic mononuclear cells, specifically resident Kupffer cells. We examined the role of VDR in acute hepatitis induced by concanavalin A (Con-A) and found that Con-A-induced hepatitis is attenuated in VDR-KO mice compared to wild-type (WT) mice. Con-A-induced hepatitis is known to be mediated by NKT cell activation, cytokine production, and reactive oxygen species (ROS) production in Kupffer cells/macrophages. However, the proportions of Kupffer cells/macrophages and the NKT cell activation were similar in the liver of WT and VDR-KO mice and inflammatory cytokine gene expression was increased in VDR-KO mice. On the other hand, plasma and hepatic ROS levels were decreased in the liver of VDR-KO mice compared to WT mice. The phagocytic activity of resident Kupffer cells and hepatic neutrophils were also decreased in VDR-KO mice. Therefore, VDR is necessary for Con-A-induced acute hepatitis and plays an important role in hepatic immune cell functions.

Lack of Vitamin D Receptor Leads to Hyperfunction of Claudin-2 in Intestinal Inflammatory Responses

BACKGROUND

Vitamin D3 and vitamin D receptor (VDR) are involved in the pathogenesis of inflammatory bowel disease (IBD) and bacterial infection. Claudin-2 is a junction protein that mediates paracellular water transport in epithelia. Elevation of Claudin-2 is associated with active IBD. However, VDR involved in epithelial junctions under inflammation and infection remains largely unknown. We investigated the mechanisms on how VDR and Claudin-2 are related in inflamed states.

METHODS

Using cultured VDR-/- enteroids, human intestinal epithelial cells, VDR-/- mice with Salmonella- or DSS-colitis, and human IBD samples, we investigated the mechanisms how VDR and Claudin-2 are related in inflamed states.

RESULTS

After Salmonella infection had taken place, we observed significantly enhanced Claudin-2 and an increased bacterial invasion and translocation. A lack of VDR regulation led to a robust increase of Claudin-2 at the mRNA and protein levels post-infection. In DSS-treated VDR-/- mice, Claudin-2 was significantly increased. Location and quantification of Claudin-2 protein in the mouse colons treated with DSS also confirmed these results. Inflammatory cytokines were significantly higher in the serum and mRNA levels in intestine, which are known to increase Claudin-2. Furthermore, in inflamed intestine of ulcerative colitis patients, VDR expression was low and Claudin-2 was enhanced. Mechanistically, we identified the enhanced Claudin-2 promoter activity through the binding sites of NF-κB and STAT in inflamed VDR-/- cells.

CONCLUSIONS

Our studies have identified a new role for intestinal epithelial VDR in regulating barrier functions in the context of infection and inflammation.

Vitamin D and liver fibrosis: Molecular mechanisms and clinical studies

Vitamin D plays a primary role in regulation of bone metabolism and calcium homeostasis. Interestingly, emerging evidence suggests protective effects of vitamin D against liver fibrogenesis. However, the precise mechanisms of this action remain mysterious. Herein, this review aimed to summarize the role of vitamin D in liver fibrosis pathology and to update the current comprehensive knowledge regarding the clinical utility of vitamin D-based treatment in liver fibrosis. In regard to its effect on liver fibrosis, vitamin D possesses an anti-fibrotic effect on hepatic stellate cells via vitamin D receptor-mediated specific signal transduction pathways, which in turn inhibit expression of pro-fibrogenic genes. Furthermore, several studies demonstrated a significant association between low vitamin D levels and an increased risk of liver fibrosis. Additionally, high prevalence of vitamin D deficiency was noted in patients with liver fibrosis, suggesting the use of vitamin D status as a biochemical marker reflecting the progression of liver fibrosis. It is therefore reasonable to postulate that vitamin D supplementation being a cost effective and relative simple procedure may benefit to liver fibrosis. Nevertheless, further research is needed to fully elucidate its regulatory role in inhibiting liver fibrogenesis and to estimate the safety and efficiency of vitamin D supplementation as a relatively inexpensive treatment for liver fibrosis in patients with chronic liver diseases.

Adaptive homeostasis of the vitamin D-vitamin D nuclear receptor axis in 8-methoxypsoralen-induced hepatotoxicity

8-methoxypsoralen (8-MOP) with ultraviolet A radiation therapy (PUVA) is the standard therapy for patients with psoriasis, despite the reported potential risks of 8-MOP-induced cholestatic liver injury in both humans and animals. Usually, patients with chronic cholestasis exhibit lower serum 25-hydroxy vitamin D (25(OH)D) levels. But those patients receiving PUVA for psoriasis showed an increase in serum 25(OH)D levels, probably highlighting that the vitamin D-vitamin D nuclear receptor (VD-VDR) axis play a protective role in 8-MOP-induced hepatotoxicity. The present study confirmed 8-MOP could increase serum 25(OH)D levels in conventional lighting and diet (CLD) and vitamin D deficient (VDD) Sprague-Dawley rats. Potential liver risks were also found in CLD and VDD rats after 8-MOP treatment. We proved that 8-MOP could be a potent ligand for VDR using molecular docking and luciferase report assay. Effect of 8-MOP on VDR subcellular distribution was determined using human liver cell line L02. We found 8-MOP could increase VDR protein expression in the nuclear and cytosol extracts and also total cell extracts in L02. siRNAs for VDR were used to determine the role of VDR in protecting 8-MOP-induced cholestasis and potential cellular mechanisms. The results showed 8-MOP could affect the CYP7A1, SHP and MRP3 expression via VDR, and such effects could be reversed by knockdown of VDR expression, suggesting a vital role of VDR involved in 8-MOP-regulated bile acid synthesis and transportation. In conclusion, these results revealed activation of VD-VDR axis may play a beneficial role in 8-MOP-mediated regulation of bile acid synthesis and transportation.

Liver X receptors regulate hepatic F4/80 + CD11b+ Kupffer cells/macrophages and innate immune responses in mice

The liver X receptors (LXRs), LXRα and LXRβ, are nuclear receptors that regulate lipid homeostasis. LXRs also regulate inflammatory responses in cultured macrophages. However, the role of LXRs in hepatic immune cells remains poorly characterized. We investigated the role of LXRs in regulation of inflammatory responses of hepatic mononuclear cells (MNCs) in mice. Both LXRα and LXRβ were expressed in mouse hepatic MNCs and F4/80⁺ Kupffer cells/macrophages. LXRα/β-knockout (KO) mice had an increased number of hepatic MNCs and elevated expression of macrophage surface markers and inflammatory cytokines compared to wild-type (WT) mice. Among MNCs, F4/80⁺CD11b⁺ cells, not F4/80⁺CD11b^- or F4/80⁺CD68⁺ cells, were increased in LXRα/β-KO mice more than WT mice. Isolated hepatic MNCs and F4/80⁺CD11b⁺ cells of LXRα/β-KO mice showed enhanced production of inflammatory cytokines after stimulation by lipopolysaccharide or CpG-DNA compared to WT cells, and LXR ligand treatment suppressed lipopolysaccharide-induced cytokine expression in hepatic MNCs. Lipopolysaccharide administration also stimulated inflammatory cytokine production in LXRα/β-KO mice more effectively than WT mice. Thus, LXR deletion enhances recruitment of F4/80⁺CD11b⁺ Kupffer cells/macrophages and acute immune responses in the liver. LXRs regulate the Kupffer cell/macrophage population and innate immune and inflammatory responses in mouse liver.

Dysregulation of Kupffer Cells/Macrophages and Natural Killer T Cells in Steatohepatitis in LXRα Knockout Male Mice

Liver X receptor (LXR) α expression is mainly localized to metabolic tissues, such as the liver, whereas LXRβ is ubiquitously expressed. LXRα is activated by oxysterols and plays an important role in the regulation of lipid metabolism in metabolic tissues. In macrophages, LXRs stimulate reverse cholesterol transport and regulate immune responses. Although a high-cholesterol diet induces severe steatohepatitis in LXRα-knockout (KO) mice, the underlying mechanisms linking lipid metabolism and immune responses remain largely unknown. In this study, we investigated the role of LXRα in the pathogenesis of steatohepatitis by assessing the effects of a high-fat and high-cholesterol diet (HFCD) on hepatic immune cell proportion and function as well as lipid metabolism in wild-type (WT) and LXRα-KO mice. HFCD feeding induced severe steatohepatitis in LXRα-KO mice compared with WT mice. These mice had higher cholesterol levels in the plasma and the liver and dysregulated expression of LXR target and proinflammatory genes in both whole liver samples and isolated hepatic mononuclear cells. Flow cytometry showed an increase in CD68+CD11b+ Kupffer cells/macrophages and a decrease in invariant natural killer T cells in the liver of HFCD-fed LXRα-KO mice. These mice were more susceptible to lipopolysaccharide-induced liver injury and resistant to inflammatory responses against α-galactosylceramide or concanavalin-A treatment. The findings provide evidence for activation of bone marrow-derived Kupffer cells/macrophages and dysfunction of invariant natural killer T cells in LXRα-KO mouse liver. These findings indicate that LXRα regulates hepatic immune function along with lipid metabolism and protects against the pathogenesis of nonalcoholic steatohepatitis.

Cytochrome P450 1A1 (CYP1A1) protects against nonalcoholic fatty liver disease caused by Western diet containing benzo[a]pyrene in mice

The Western diet contributes to nonalcoholic fatty liver disease (NAFLD) pathogenesis. Benzo[a]pyrene (BaP), a prototypical environmental pollutant produced by combustion processes, is present in charcoal-grilled meat. Cytochrome P450 1A1 (CYP1A1) metabolizes BaP, resulting in either detoxication or metabolic activation in a context-dependent manner. To elucidate a role of CYP1A1-BaP in NAFLD pathogenesis, we compared the effects of a Western diet, with or without oral BaP treatment, on the development of NAFLD in Cyp1a1(-/-) mice versus wild-type mice. A Western diet plus BaP induced lipid-droplet accumulation in liver of Cyp1a1(-/-) mice, but not wild-type mice. The hepatic steatosis observed in Cyp1a1(-/-) mice was associated with increased cholesterol, triglyceride and bile acid levels. Cyp1a1(-/-) mice fed Western diet plus BaP had changes in expression of genes involved in bile acid and lipid metabolism, and showed no increase in Cyp1a2 expression but did exhibit enhanced Cyp1b1 mRNA expression, as well as hepatic inflammation. Enhanced BaP metabolic activation, oxidative stress and inflammation may exacerbate metabolic dysfunction in liver of Cyp1a1(-/-) mice. Thus, Western diet plus BaP induces NAFLD and hepatic inflammation in Cyp1a1(-/-) mice in comparison to wild-type mice, indicating a protective role of CYP1A1 against NAFLD pathogenesis.

1α-Hydroxy derivatives of 7-dehydrocholesterol are selective liver X receptor modulators

The nuclear receptors liver X receptor (LXR) α and LXRβ are involved in the regulation of lipid metabolism, inflammation, immunity, cellular proliferation, and apoptosis. Oxysterols are endogenous LXR ligands, and also interact with other nuclear and membrane receptors. We previously reported that a phytosterol derivative with a 1α-hydroxy group acts as a potent LXR agonist with intestine-selective action and that 25-hydroxy and 26/27-hydroxy metabolites of 7-dehydrocholesterol (7-DHC) exhibit partial LXR agonism. In this study, we report that 1α-hydroxy derivatives of 7-DHC, 1α-OH-7-DHC and 1,25-(OH)₂-7-DHC, act as LXR modulators. Luciferase reporter gene assays showed that 1α-OH-7-DHC activates LXRα and LXRβ and that 1,25-(OH)₂-7-DHC activates both LXRs and vitamin D receptor. Examination of cofactor peptide association showed that the 1α-hydroxy derivatives, specifically 1,25-(OH)₂-7-DHC, induce association of coactivator/corepressor peptide in a different manner from the agonist T0901317. Docking modeling and alanine mutational analysis of LXRα demonstrated that 1,25-(OH)₂-7-DHC interacts with LXRα residues in a manner distinct from potent agonists, such as T0901317 and 24(S),25-epoxycholesterol. 1α-OH-7-DHC and 1,25-(OH)₂-7-DHC induced expression of LXR target genes in a cell type- and gene-selective manner. 1,25-(OH)₂-7-DHC effectively suppressed lipopolysaccharide-stimulated proinflammatory gene expression in an LXR-dependent manner. Therefore, 1α-hydroxy derivatives, such as 1,25-(OH)₂-7-DHC, are unique LXR modulators with selective agonistic activity and potent transrepression function. These oxysterols have potential as LXR-targeted therapeutics for inflammatory disease.

Ambient ultraviolet radiation exposure and hepatocellular carcinoma incidence in the United States

BACKGROUND

Hepatocellular carcinoma (HCC), the most commonly occurring type of primary liver cancer, has been increasing in incidence worldwide. Vitamin D, acquired from sunlight exposure, diet, and dietary supplements, has been hypothesized to impact hepatocarcinogenesis. However, previous epidemiologic studies examining the associations between dietary and serum vitamin D reported mixed results. The purpose of this study was to examine the association between ambient ultraviolet (UV) radiation exposure and HCC risk in the U.S.

METHODS

The Surveillance, Epidemiology, and End Results (SEER) database provided information on HCC cases diagnosed between 2000 and 2014 from 16 population-based cancer registries across the U.S. Ambient UV exposure was estimated by linking the SEER county with a spatiotemporal UV exposure model using a geographic information system. Poisson regression with robust variance estimation was used to calculate incidence rate ratios (IRRs) and 95% confidence intervals (CIs) for the association between ambient UV exposure per interquartile range (IQR) increase (32.4 mW/m2) and HCC risk adjusting for age at diagnosis, sex, race, year of diagnosis, SEER registry, and county-level information on prevalence of health conditions, lifestyle, socioeconomic, and environmental factors.

RESULTS

Higher levels of ambient UV exposure were associated with statistically significant lower HCC risk (n = 56,245 cases; adjusted IRR per IQR increase: 0.83, 95% CI 0.77, 0.90; p < 0.01). A statistically significant inverse association between ambient UV and HCC risk was observed among males (p for interaction = 0.01) and whites (p for interaction = 0.01).

CONCLUSIONS

Higher ambient UV exposure was associated with a decreased risk of HCC in the U.S. UV exposure may be a potential modifiable risk factor for HCC that should be explored in future research.

Emerging drugs for the treatment of Primary Biliary Cholangitis

INTRODUCTION

Primary biliary cholangitis (PBC) is an autoimmune chronic disease of the liver that can progress to cirrhosis and hepatocellular carcinoma. It affects approximately 1 in 4,000 with a 10:1 female to male ratio. The diagnosis of PBC can be made based on serum antimitochondrial antibodies (AMA) in a patient with abnormally high serum alkaline phosphatase after ruling out other causes of cholestasis and biliary obstruction. Genome-wide association studies have revealed several human leukocyte antigen (HLA) and non-HLA risk loci in PBC, and complex environmental-host immunogenetic interactions are believed to underlie the etiopathogenesis of the disease. Fatigue and pruritus are the most common and often problematic symptoms; although often mild, these can be severe and life-alternating in a subset of patients. Ursodeoxycholic acid (UDCA) is the only drug approved by the United States Food and Drug Administration for the treatment of PBC. Clinical trials have shown that UDCA significantly improves transplant-free survival. However, nearly 40% of PBC patients do not respond adequately to PBC and are at higher risk for serious complications when compared to PBC patients with complete response to UDCA.

AREAS COVERED

Here we provide a detailed discussion regarding novel therapeutic agents and potential areas for further investigation in PBC-related research.

EXPERT OPINION

Results of ongoing clinical trials and emerging treatment paradigms for PBC will likely further improve medical management of this disorder in the near future.

Nuclear Receptors as Therapeutic Targets in Liver Disease: Are We There Yet?

Nuclear receptors (NR) are ligand-modulated transcription factors that play diverse roles in cell differentiation, development, proliferation, and metabolism and are associated with numerous liver pathologies such as cancer, steatosis, inflammation, fibrosis, cholestasis, and xenobiotic/drug-induced liver injury. The network of target proteins associated with NRs is extremely complex, comprising coregulators, small noncoding microRNAs, and long noncoding RNAs. The importance of NRs as targets of liver disease is exemplified by the number of NR ligands that are currently used in the clinics or in clinical trials with promising results. Understanding the regulation by NR during pathophysiological conditions, and identifying ligands for orphan NR, points to a potential therapeutic approach for patients with liver diseases. An overview of complex NR metabolic networks and their pharmacological implications in liver disease is presented here.

Pharmacology of bile acid receptors: Evolution of bile acids from simple detergents to complex signaling molecules

For many years, bile acids were thought to only function as detergents which solubilize fats and facilitate the uptake of fat-soluble vitamins in the intestine. Many early observations; however, demonstrated that bile acids regulate more complex processes, such as bile acids synthesis and immune cell function through activation of signal transduction pathways. These studies were the first to suggest that receptors may exist for bile acids. Ultimately, seminal studies by many investigators led to the discovery of several bile acid-activated receptors including the farnesoid X receptor, the vitamin D receptor, the pregnane X receptor, TGR5, α5 β1 integrin, and sphingosine-1-phosphate receptor 2. Several of these receptors are expressed outside of the gastrointestinal system, indicating that bile acids may have diverse functions throughout the body. Characterization of the functions of these receptors over the last two decades has identified many important roles for these receptors in regulation of bile acid synthesis, transport, and detoxification; regulation of glucose utilization; regulation of fatty acid synthesis and oxidation; regulation of immune cell function; regulation of energy expenditure; and regulation of neural processes such as gastric motility. Through these many functions, bile acids regulate many aspects of digestion ranging from uptake of essential vitamins to proper utilization of nutrients. Accordingly, within a short time period, bile acids moved beyond simple detergents and into the realm of complex signaling molecules. Because of the important processes that bile acids regulate through activation of receptors, drugs that target these receptors are under development for the treatment of several diseases, including cholestatic liver disease and metabolic syndrome. In this review, we will describe the various bile acid receptors, the signal transduction pathways activated by these receptors, and briefly discuss the physiological processes that these receptors regulate.

Tight junction CLDN2 gene is a direct target of the vitamin D receptor

The breakdown of the intestinal barrier is a common manifestation of many diseases. Recent evidence suggests that vitamin D and its receptor VDR may regulate intestinal barrier function. Claudin-2 is a tight junction protein that mediates paracellular water transport in intestinal epithelia, rendering them “leaky”. Using whole body VDR^-/- mice, intestinal epithelial VDR conditional knockout (VDR^ΔIEC) mice, and cultured human intestinal epithelial cells, we demonstrate here that the CLDN2 gene is a direct target of the transcription factor VDR. The Caudal-Related Homeobox (Cdx) protein family is a group of the transcription factor proteins which bind to DNA to regulate the expression of genes. Our data showed that VDR-enhances Claudin-2 promoter activity in a Cdx1 binding site-dependent manner. We further identify a functional vitamin D response element (VDRE) 5΄-AGATAACAAAGGTCA-3΄ in the Cdx1 site of the Claudin-2 promoter. It is a VDRE required for the regulation of Claudin-2 by vitamin D. Absence of VDR decreased Claudin-2 expression by abolishing VDR/promoter binding. In vivo, VDR deletion in intestinal epithelial cells led to significant decreased Claudin-2 in VDR^-/- and VDR^ΔIEC mice. The current study reveals an important and novel mechanism for VDR by regulation of epithelial barriers.

Serum vitamin D level is associated with disease severity and response to ursodeoxycholic acid in primary biliary cirrhosis

BACKGROUND

Serum vitamin D levels are associated with bone complications in patients with primary biliary cirrhosis (PBC). Increasing evidence suggests a nonskeletal role of vitamin D in various autoimmune and liver diseases.

AIM

To investigate the clinical relevance of vitamin D levels in PBC, especially their association with the therapeutic effects of ursodeoxycholic acid (UDCA).

METHODS

Consecutive PBC patients were retrospectively reviewed. 25-hydroxyvitamin D [25(OH)D] levels were determined in frozen serum samples collected before initiation of UDCA treatment. Response to UDCA was evaluated by Paris-I and Barcelona criteria. Logistic regressions were performed to identify the treatment response-associated parameters.

RESULTS

Among 98 patients, the mean serum 25(OH)D concentration was 17.9 ± 7.6 ng/mL. 25(OH)D levels decreased with increasing histological stage (P = 0.029) and were negatively correlated with bilirubin and alkaline phosphatase levels. After 1 year of UDCA therapy, 31 patients failed to achieve complete response according to Paris-I criteria. The baseline 25(OH)D level was significantly lower in nonresponders (14.8 ± 6.4 vs. 19.3 ± 7.6 ng/mL, P = 0.005). Vitamin D deficiency at baseline was associated with an increased risk of incomplete response independent of advanced stages (OR = 3.93, 95% CI = 1.02-15.19, P = 0.047). Similar results were obtained when biochemical response was evaluated by Barcelona criteria. Furthermore, 25(OH)D levels were lower in patients who subsequently suffered death or liver transplantation (12.1 ± 4.6 vs. 18.4 ± 7.6 ng/mL, P = 0.023).

CONCLUSIONS

25(OH)D level is associated with biochemical and histological features in PBC. Pre-treatment vitamin D status is independently related to subsequent response to UDCA. Our results suggest that vitamin D status may have important clinical significance in PBC.

Bile Acid Metabolism and Signaling in Cholestasis, Inflammation, and Cancer

Bile acids are synthesized from cholesterol in the liver. Some cytochrome P450 (CYP) enzymes play key roles in bile acid synthesis. Bile acids are physiological detergent molecules, so are highly cytotoxic. They undergo enterohepatic circulation and play important roles in generating bile flow and facilitating biliary secretion of endogenous metabolites and xenobiotics and intestinal absorption of dietary fats and lipid-soluble vitamins. Bile acid synthesis, transport, and pool size are therefore tightly regulated under physiological conditions. In cholestasis, impaired bile flow leads to accumulation of bile acids in the liver, causing hepatocyte and biliary injury and inflammation. Chronic cholestasis is associated with fibrosis, cirrhosis, and eventually liver failure. Chronic cholestasis also increases the risk of developing hepatocellular or cholangiocellular carcinomas. Extensive research in the last two decades has shown that bile acids act as signaling molecules that regulate various cellular processes. The bile acid-activated nuclear receptors are ligand-activated transcriptional factors that play critical roles in the regulation of bile acid, drug, and xenobiotic metabolism. In cholestasis, these bile acid-activated receptors regulate a network of genes involved in bile acid synthesis, conjugation, transport, and metabolism to alleviate bile acid-induced inflammation and injury. Additionally, bile acids are known to regulate cell growth and proliferation, and altered bile acid levels in diseased conditions have been implicated in liver injury/regeneration and tumorigenesis. We will cover the mechanisms that regulate bile acid homeostasis and detoxification during cholestasis, and the roles of bile acids in the initiation and regulation of hepatic inflammation, regeneration, and carcinogenesis.

Bile acid signaling in metabolic disease and drug therapy

Bile acids are the end products of cholesterol catabolism. Hepatic bile acid synthesis accounts for a major fraction of daily cholesterol turnover in humans. Biliary secretion of bile acids generates bile flow and facilitates hepatobiliary secretion of lipids, lipophilic metabolites, and xenobiotics. In the intestine, bile acids are essential for the absorption, transport, and metabolism of dietary fats and lipid-soluble vitamins. Extensive research in the last 2 decades has unveiled new functions of bile acids as signaling molecules and metabolic integrators. The bile acid-activated nuclear receptors farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, vitamin D receptor, and G protein-coupled bile acid receptor play critical roles in the regulation of lipid, glucose, and energy metabolism, inflammation, and drug metabolism and detoxification. Bile acid synthesis exhibits a strong diurnal rhythm, which is entrained by fasting and refeeding as well as nutrient status and plays an important role for maintaining metabolic homeostasis. Recent research revealed an interaction of liver bile acids and gut microbiota in the regulation of liver metabolism. Circadian disturbance and altered gut microbiota contribute to the pathogenesis of liver diseases, inflammatory bowel diseases, nonalcoholic fatty liver disease, diabetes, and obesity. Bile acids and their derivatives are potential therapeutic agents for treating metabolic diseases of the liver.

Comparative portal hypotensive effects as propranolol of vitamin D₃ treatment by decreasing intrahepatic resistance in cirrhotic rats

BACKGROUND AND AIM

Vitamin D₃ improves portal hypertension (PH) through the activation of vitamin D receptor (VDR) and calcium-sensing receptor (CaSR) in cirrhotic rats. Propranolol is a non-selective β-blocker that is recommended for the treatment of PH. The present study aims to investigate the detail systemic and hepatic mechanisms of vitamin D₃ and propranolol, alone or in combination, in cirrhotic rats.

METHODS

Common bile duct-ligated and thioacetamide cirrhotic rats were treated with vehicle, propranolol (30 mg/kg/day), vitamin D₃ (0.5 μg/100 g/day, twice weekly), or propranolol + vitamin D₃, separately.

RESULTS

Significantly, propranolol and vitamin D₃ produced a similar magnitude of reduction in portal venous pressure (PVP) in cirrhotic rats through different mechanisms: whereas propranolol decreased PVP by reducing splanchnic hyperemia and cardiac index, vitamin D₃ decreased PVP by decreasing intrahepatic resistance (IHR). However, propranolol + vitamin D₃ did not further decrease PVP in cirrhotic rats. Notably, a marked decrease in hepatic VDR and CaSR expressions was noted in cirrhotic human/rat livers compared with non-cirrhotic human/rat livers. In cirrhotic rats, vitamin D₃ administration decreasing IHR by inhibiting the renin-angiotensin system, hepatic oxidative stress, inflammation/fibrosis, angiotensin II (ANGII) production, CaSR-mediated ANGII hyperresponsiveness, ANGII-induced hepatic stellate cells contraction, and correcting hepatic endothelial dysfunction through upregulation of hepatic VDR, CaSR, and endothelial nitric oxide synthase expressions.

CONCLUSION

Chronic vitamin D₃ treatment alone results in comparative portal hypotensive effects as propranolol alone in cirrhotic rats with PH. Taken together, chronic vitamin D₃ administration was an ideal alternative strategy to effectively improve PH without unwanted systemic side-effects.

The immunomodulatory role of bile acids

Enzymatic oxidation of cholesterol generates numerous distinct bile acids which function both as detergents that facilitate the digestion and absorption of dietary lipids and as hormones that activate five distinct receptors. Activation of these receptors alters gene expression in multiple tissues, leading to changes not only in bile acid metabolism but also in glucose homeostasis, lipid and lipoprotein metabolism, energy expenditure, intestinal motility, bacterial growth, inflammation, and in the liver-gut axis. This review focuses on the present knowledge regarding the physiologic and pathologic role of bile acids and their immunomodulatory role, with particular attention to bacterial lipopolysaccharides (endotoxins) and bile acid and immunological disorders. The specific role that bile acids play in the regulation of innate immunity, various systemic inflammations, inflammatory bowel diseases, allergy, psoriasis, cholestasis, obesity, metabolic syndrome, alcoholic liver disease, and colon cancer will be reviewed.

Prediagnostic circulating vitamin D levels and risk of hepatocellular carcinoma in European populations: a nested case-control study

The association between vitamin D status and hepatocellular carcinoma (HCC) has not been well investigated, despite experimental evidence supporting an important role of vitamin D in liver pathophysiology. Our objective was to investigate the association between prediagnostic circulating 25-hydroxyvitamin D [25(OH)D] serum levels and the risk of HCC in a prospective, nested case-control study among 520,000 participants in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. Each case (n = 138) diagnosed between 1992 and 2010 was matched to one control by age, sex, study center, date and time of blood collection, and fasting status. Serum baseline levels of 25(OH)D were measured by liquid chromatography/tandem mass spectrometry. Multivariable incident rate ratios (IRRs) of HCC associated with continuous (per 10 nmol/L) or categorical levels (tertiles or a priori-defined categories) of prediagnostic 25(OH)D were calculated using conditional logistic regression. Higher 25(OH)D levels were associated with a 49% reduction in the risk of HCC (highest versus lowest tertile: multivariable IRR = 0.51, 95% confidence interval [CI], 0.26 to 0.99; Ptrend  = 0.04; per 10 nmol/L increase: IRR = 0.80, 95% CI, 0.68-0.94). The finding did not vary substantially by time from enrolment to diagnosis, and did not change after adjustment for biomarkers of preexisting liver damage, nor chronic infection with hepatitis B or C viruses. The findings were not modified by body size or smoking status.

CONCLUSION

In this prospective study on western European populations, serum levels of 25(OH)D were inversely associated with the risk of HCC. Given the rising incidence of this cancer in low-risk developed countries and the strong public health interest surrounding the potentially cancer-protective roles of vitamin D, additional studies in different populations are required.

Clinical application of transcriptional activators of bile salt transporters

Hepatobiliary bile salt (BS) transporters are critical determinants of BS homeostasis controlling intracellular concentrations of BSs and their enterohepatic circulation. Genetic or acquired dysfunction of specific transport systems causes intrahepatic and systemic retention of potentially cytotoxic BSs, which, in high concentrations, may disturb integrity of cell membranes and subcellular organelles resulting in cell death, inflammation and fibrosis. Transcriptional regulation of canalicular BS efflux through bile salt export pump (BSEP), basolateral elimination through organic solute transporters alpha and beta (OSTα/OSTβ) as well as inhibition of hepatocellular BS uptake through basolateral Na(+)-taurocholate cotransporting polypeptide (NTCP) represent critical steps in protection from hepatocellular BS overload and can be targeted therapeutically. In this article, we review the potential clinical implications of the major BS transporters BSEP, OSTα/OSTβ and NTCP in the pathogenesis of hereditary and acquired cholestatic syndromes, provide an overview on transcriptional control of these transporters by the key regulatory nuclear receptors and discuss the potential therapeutic role of novel transcriptional activators of BS transporters in cholestasis.

Vitamin D receptor activation down-regulates the small heterodimer partner and increases CYP7A1 to lower cholesterol

BACKGROUND & AIMS

Little is known about the effects of the vitamin D receptor (VDR) on hepatic activity of human cholesterol 7α-hydroxylase (CYP7A1) and cholesterol metabolism. We studied these processes in mice in vivo and mouse and human hepatocytes.

METHODS

Farnesoid X receptor (Fxr)(-/-), small heterodimer partner (Shp)(-/-), and C57BL/6 (wild-type control) mice were fed normal or Western diets for 3 weeks and were then given intraperitoneal injections of vehicle (corn oil) or 1α,25-dihydroxyvitamin D3 (1,25[OH]2D3; 4 doses, 2.5 μg/kg, every other day). Plasma and tissue samples were collected and levels of Vdr, Shp, Cyp7a1, Cyp24a1, and rodent fibroblast growth factor (Fgf) 15 expression, as well as levels of cholesterol, were measured. We studied the regulation of Shp by Vdr using reporter and mobility shift assays in transfected human embryonic kidney 293 cells, quantitative polymerase chain reaction with mouse tissues and mouse and human hepatocytes, and chromatin immunoprecipitation assays with mouse liver.

RESULTS

We first confirmed the presence of Vdr mRNA and protein expression in livers of mice. In mice fed normal diets and given injections of 1,25(OH)2D3, liver and plasma concentrations of 1,25(OH)2D3 increased and decreased in unison. Changes in hepatic Cyp7a1 messenger RNA (mRNA) correlated with those of Cyp24a1 (a Vdr target gene) and inversely with Shp mRNA, but not ileal Fgf15 mRNA. Similarly, incubation with 1,25(OH)2D3 increased levels of Cyp24a1/CYP24A1 and Cyp7a1/CYP7A1 mRNA in mouse and human hepatocytes, and reduced levels of Shp mRNA in mouse hepatocytes. In Fxr(-/-) and wild-type mice with hypercholesterolemia, injection of 1,25(OH)2D3 consistently reduced levels of plasma and liver cholesterol and Shp mRNA, and increased hepatic Cyp7a1 mRNA and protein; these changes were not observed in Shp(-/-) mice given 1,25(OH)2D3 and fed Western diets. Truncation of the human small heterodimer partner (SHP) promoter and deletion analyses revealed VDR-dependent inhibition of SHP, and mobility shift assays showed direct binding of VDR to enhancer regions of SHP. In addition, chromatin immunoprecipitation analysis of livers from mice showed that injection of 1,25(OH)2D3 increased recruitment of Vdr and rodent retinoid X receptor to the Shp promoter.

CONCLUSIONS

Activation of the VDR represses hepatic SHP to increase levels of mouse and human CYP7A1 and reduce cholesterol.

Bile acid receptors as targets for drug development

The intracellular nuclear receptor farnesoid X receptor and the transmembrane G protein-coupled receptor TGR5 respond to bile acids by activating transcriptional networks and/or signalling cascades. These cascades affect the expression of a great number of target genes relevant for bile acid, cholesterol, lipid and carbohydrate metabolism, as well as genes involved in inflammation, fibrosis and carcinogenesis. Pregnane X receptor, vitamin D receptor and constitutive androstane receptor are additional nuclear receptors that respond to bile acids, albeit to a more restricted set of species of bile acids. Recognition of dedicated bile acid receptors prompted the development of semi-synthetic bile acid analogues and nonsteroidal compounds that target these receptors. These agents hold promise to become a new class of drugs for the treatment of chronic liver disease, hepatocellular cancer and extrahepatic inflammatory and metabolic diseases. This Review discusses the relevant bile acid receptors, the new drugs that target bile acid signalling and their possible applications.

Intestinal CYP3A4 protects against lithocholic acid-induced hepatotoxicity in intestine-specific VDR-deficient mice

Vitamin D receptor (VDR) mediates vitamin D signaling involved in bone metabolism, cellular growth and differentiation, cardiovascular function, and bile acid regulation. Mice with an intestine-specific disruption of VDR (Vdr(ΔIEpC)) have abnormal body size, colon structure, and imbalance of bile acid metabolism. Lithocholic acid (LCA), a secondary bile acid that activates VDR, is among the most toxic of the bile acids that when overaccumulated in the liver causes hepatotoxicity. Because cytochrome P450 3A4 (CYP3A4) is a target gene of VDR-involved bile acid metabolism, the role of CYP3A4 in VDR biology and bile acid metabolism was investigated. The CYP3A4 gene was inserted into Vdr(ΔIEpC) mice to produce the Vdr(ΔIEpC)/3A4 line. LCA was administered to control, transgenic-CYP3A4, Vdr(ΔIEpC), and Vdr(ΔIEpC)/3A4 mice, and hepatic toxicity and bile acid levels in the liver, intestine, bile, and urine were measured. VDR deficiency in the intestine of the Vdr(ΔIEpC) mice exacerbates LCA-induced hepatotoxicity manifested by increased necrosis and inflammation, due in part to over-accumulation of hepatic bile acids including taurocholic acid and taurodeoxycholic acid. Intestinal expression of CYP3A4 in the Vdr(ΔIEpC)/3A4 mouse line reduces LCA-induced hepatotoxicity through elevation of LCA metabolism and detoxification, and suppression of bile acid transporter expression in the small intestine. This study reveals that intestinal CYP3A4 protects against LCA hepatotoxicity.

Vitamin D nuclear receptor deficiency promotes cholestatic liver injury by disruption of biliary epithelial cell junctions in mice

Alterations in apical junctional complexes (AJCs) have been reported in genetic or acquired biliary diseases. The vitamin D nuclear receptor (VDR), predominantly expressed in biliary epithelial cells in the liver, has been shown to regulate AJCs. The aim of our study was thus to investigate the role of VDR in the maintenance of bile duct integrity in mice challenged with biliary-type liver injury. Vdr(-/-) mice subjected to bile duct ligation (BDL) displayed increased liver damage compared to wildtype BDL mice. Adaptation to cholestasis, ascertained by expression of genes involved in bile acid metabolism and tissue repair, was limited in Vdr(-/-) BDL mice. Furthermore, evaluation of Vdr(-/-) BDL mouse liver tissue sections indicated altered E-cadherin staining associated with increased bile duct rupture. Total liver protein analysis revealed that a truncated form of E-cadherin was present in higher amounts in Vdr(-/-) mice subjected to BDL compared to wildtype BDL mice. Truncated E-cadherin was also associated with loss of cell adhesion in biliary epithelial cells silenced for VDR. In these cells, E-cadherin cleavage occurred together with calpain 1 activation and was prevented by the silencing of calpain 1. Furthermore, VDR deficiency led to the activation of the epidermal growth factor receptor (EGFR) pathway, while EGFR activation by EGF induced both calpain 1 activation and E-cadherin cleavage in these cells. Finally, truncation of E-cadherin was blunted when EGFR signaling was inhibited in VDR-silenced cells.

CONCLUSION

Biliary-type liver injury is exacerbated in Vdr(-/-) mice by limited adaptive response and increased bile duct rupture. These results indicate that loss of VDR restricts the adaptation to cholestasis and diminishes bile duct integrity in the setting of biliary-type liver injury.

Nuclear receptors in bile acid metabolism

Bile acids are signaling molecules that activate nuclear receptors, such as farnesoid X receptor, pregnane X receptor, constitutive androstane receptor, and vitamin D receptor, and play a critical role in the regulation of lipid, glucose, energy, and drug metabolism. These xenobiotic/endobiotic-sensing nuclear receptors regulate phase I oxidation, phase II conjugation, and phase III transport in bile acid and drug metabolism in the digestive system. Integration of bile acid metabolism with drug metabolism controls absorption, transport, and metabolism of nutrients and drugs to maintain metabolic homeostasis and also protects against liver injury, inflammation, and related metabolic diseases, such as nonalcoholic fatty liver disease, diabetes, and obesity. Bile-acid-based drugs targeting nuclear receptors are in clinical trials for treating cholestatic liver diseases and fatty liver disease.

Nuclear receptors as drug targets in cholestatic liver diseases

Cholestatic liver diseases encompass a wide spectrum of disorders with different causes, resulting in impaired bile flow and accumulation of bile acids and other potentially hepatotoxic cholephils. The understanding of the molecular mechanisms of bile formation and cholestasis has recently improved significantly through new insights into nuclear receptor (patho)biology. Nuclear receptors are ligand-activated transcription factors, which act as central players in the regulation of genes responsible for elimination and detoxification of biliary constituents accumulating in cholestasis. They also control other pathophysiologic processes such as inflammation, fibrogenesis, and carcinogenesis involved in the pathogenesis and disease progression of cholestasis liver diseases.