Bile acids for viral hepatitis

Advances in Immunotherapy for Hepatitis B

Hepatitis B virus (HBV) is a hepatotropic virus with the potential to cause chronic infection, and it is one of the common causes of liver disease worldwide. Chronic HBV infection leads to liver cirrhosis and, ultimately, hepatocellular carcinoma (HCC). The persistence of covalently closed circular DNA (cccDNA) and the impaired immune response in patients with chronic hepatitis B (CHB) has been studied over the past few decades. Despite advances in the etiology of HBV and the development of potent virus-suppressing regimens, a cure for HBV has not been found. Both the innate and adaptive branches of immunity contribute to viral eradication. However, immune exhaustion and evasion have been demonstrated during CHB infection, although our understanding of the mechanism is still evolving. Recently, the successful use of an antiviral drug for hepatitis C has greatly encouraged the search for a cure for hepatitis B, which likely requires an approach focused on improving the antiviral immune response. In this review, we discuss our current knowledge of the immunopathogenic mechanisms and immunobiology of HBV infection. In addition, we touch upon why the existing therapeutic approaches may not achieve the goal of a functional cure. We also propose how combinations of new drugs, and especially novel immunotherapies, contribute to HBV clearance.

Structural Basis for Human Norovirus Capsid Binding to Bile Acids

A recently developed human norovirus cell culture system revealed that the presence of bile enhanced or was an essential requirement for the growth of certain genotypes. Before this discovery, histo-blood group antigens (HBGAs) were the only well-studied cofactor known for human noroviruses, and there was evidence that several genotypes poorly bound HBGAs. Therefore, the purpose of this study was to investigate how human norovirus capsids interact with bile acids. We found that bile acids had low-micromolar affinities for GII.1, GII.10, and GII.19 capsids but did not bind GI.1, GII.3, GII.4, or GII.17. We showed that bile acid bound at a partially conserved pocket on the norovirus capsid-protruding (P) domain using X-ray crystallography. Amino acid sequence alignment and structural analysis delivered an explanation of selective bile acid binding. Intriguingly, we discovered that binding of the bile acid was the critical step to stabilize several P domain loops that optimally placed an essential amino acid side chain (Asp375) to bind HBGAs in an otherwise HBGA nonbinder (GII.1). Furthermore, bile acid enhanced HBGA binding for a known HBGA binder (GII.10). Altogether, these new data suggest that bile acid functions as a loop-stabilizing regulator and enhancer of HBGA binding for certain norovirus genotypes.IMPORTANCE Given that human norovirus virions likely interact with bile acid during a natural infection, our evidence that an HBGA nonbinder (GII.1) can be converted to an HBGA binder after bile acid binding is of major significance. Our data provide direct evidence that, like HBGAs, bile acid interaction on the capsid is an important cofactor for certain genotypes. However, more unanswered questions seem to arise from these new discoveries. For example, is there an association between the bile acid requirement and the prevalence of certain genotypes? That is, the GII.1 and GII.10 (bile acid binders) genotypes rarely caused outbreaks, whereas the GII.4 and GII.17 genotypes (bile acid nonbinders) were responsible for large epidemics. Therefore, it seems plausible that certain genotypes require bile acids, whereas others have modified their bile acid requirements on the capsid.

Ursodeoxycholic Acid in Treatment of Non-cholestatic Liver Diseases: A Systematic Review

Aims: To systematically evaluate the literature for evidence to support the use of bile acids in non-cholestatic liver conditions. Methods: Searches were conducted on the databases of Medline (1948-March 31, 2015), Embase (1980-March 31, 2015) and the Cochrane Central Register of Controlled Trials, and on Google and Google Scholar to identify articles describing ursodeoxycholic acid (UDCA) and its derivatives for non-cholestatic hepatic indications. Combinations of the following search terms were used: ursodeoxycholic acid, ursodiol, bile acids and/or salts, non alcoholic fatty liver, non alcoholic steatohepatitis, fatty liver, alcoholic hepatitis, alcohol, liver disease, autoimmune, autoimmune hepatitis, liver transplant, liver graft, transplant rejection, graft rejection, ischemic reperfusion injury, reperfusion injury, hepatitis B, hepatitis C, viral hepatitis, chronic hepatitis, acute hepatitis, transaminases, alanine transaminase, liver enzymes, aspartate aminotransferase, gamma-glutamyl transferase, gamma-glutamyl transpeptidase, bilirubin, alkaline phosphatase. No search limits were applied. Additionally, references of the included studies were reviewed to identify additional articles. Results: The literature search yielded articles meeting inclusion criteria for the following indications: non-alcoholic fatty liver disease (n = 5); alcoholic liver disease (n = 2); autoimmune hepatitis (n = 6), liver transplant (n = 2) and viral hepatitis (n = 9). Bile acid use was associated with improved normalization of liver biochemistry in non-alcoholic fatty liver disease, autoimmune hepatitis and hepatitis B and C infections. In contrast, liver biochemistry normalization was inconsistent in alcoholic liver disease and liver transplantation. The majority of studies reviewed showed that normalization of liver biochemistry did not correlate to improvement in histologic disease. In the prospective trials reviewed, adverse effects associated with the bile acids were limited to minor gastrointestinal complaints (most often, diarrhea) and did not occur at increased frequency as compared to controls. As administration of bile acids was often limited to durations of 12 months or less, long-term side effects for non-cholestatic indications cannot be excluded. Conclusions: Based on the available literature, bile acids cannot be widely recommended for non-cholestatic liver diseases at present.

A network meta-analysis of the efficacy and side effects of UDCA-based therapies for primary sclerosing cholangitis

OBJECTIVES

Therapies for treatment of patients with primary sclerosing cholangitis (PSC) include administration of ursodeoxycholic acid (UDCA) alone, or combination with metronidazole (MTZ) or mycophenolate mofetil (MMF), respectively. However, the optimum regimen still remains inconclusive. We aimed to compare interventions in terms of patient mortality or liver transplantation (MOLT), progression of liver histological stage (POLHS), serum bilirubin, alkaline phosphatase (ALP) levels and adverse events (AE).

METHODS

We searched PubMed, Embase and the Cochrane Library for randomized controlled trials until 31, Jan 2015. We estimated hazard ratios (HRs), odds ratios (ORs) and mean difference (MD) between treatments on clinical outcomes. Sensitivity analyses based on the dose of UDCA, quality of trials or treatment duration were also performed.

RESULTS

Ten RCTs were included. Compared with UDCA plus MTZ, UDCA (HR 0.28, 95%CI 0.01-3.41), UDCA plus MMF (HR 0.08, 95%CI 0.00-4.18), or OBS (HR 0.28, 95%CI 0.01-3.98) all provided an increased risk of MOLT. UDCA provided a significant reduction in bilirubin and ALP levels compared with OBS (MD -13.92, P < 0.001; MD -484.34, P < 0.001; respectively). With respect to POLHS, although differing not significantly, UDCA plus MTZ had a tendency to improve LHS more than UDCA (OR 1.33), UDCA plus MMF (OR 3.24) or OBS (OR 1.08). Additionally, UDCA plus MTZ (MD -544.66, P < 0.001) showed a significant reduction in ALP levels compared with OBS, but appeared to be associated with more AEs compared with UDCA (OR 5.09), UDCA plus MMF (OR 4.80) or OBS (OR 7.21).

CONCLUSIONS

MTZ plus UDCA was the most effective therapy in survival rates and liver histological progression.

Primary biliary acids inhibit hepatitis D virus (HDV) entry into human hepatoma cells expressing the sodium-taurocholate cotransporting polypeptide (NTCP)

BACKGROUND

The sodium-taurocholate cotransporting polypeptide (NTCP) is both a key bile acid (BA) transporter mediating uptake of BA into hepatocytes and an essential receptor for hepatitis B virus (HBV) and hepatitis D virus (HDV). In this study we aimed to characterize to what extent and through what mechanism BA affect HDV cell entry.

METHODS

HuH-7 cells stably expressing NTCP (HuH-7/NTCP) and primary human hepatocytes (PHH) were infected with in vitro generated HDV particles. Infectivity in the absence or presence of compounds was assessed using immunofluorescence staining for HDV antigen, standard 50% tissue culture infectious dose (TCID50) assays and quantitative PCR.

RESULTS

Addition of primary conjugated and unconjugated BA resulted in a dose dependent reduction in the number of infected cells while secondary, tertiary and synthetic BA had a lesser effect. This effect was observed both in HuH-7/NTCP and in PHH. Other replication cycle steps such as replication and particle assembly and release were unaffected. Moreover, inhibitory BA competed with a fragment from the large HBV envelope protein for binding to NTCP-expressing cells. Conversely, the sodium/BA-cotransporter function of NTCP seemed not to be required for HDV infection since infection was similar in the presence or absence of a sodium gradient across the plasma membrane. When chenodeoxycolic acid (15 mg per kg body weight) was administered to three chronically HDV infected individuals over a period of up to 16 days there was no change in serum HDV RNA.

CONCLUSIONS

Primary BA inhibit NTCP-mediated HDV entry into hepatocytes suggesting that modulation of the BA pool may affect HDV infection of hepatocytes.

Kinetics of the bile acid transporter and hepatitis B virus receptor Na+/taurocholate cotransporting polypeptide (NTCP) in hepatocytes

BACKGROUND & AIMS

The human liver bile acid transporter Na(+)/taurocholate cotransporting polypeptide (NTCP) has recently been identified as liver-specific receptor for infection of hepatitis B virus (HBV), which attaches via the myristoylated preS1 (myr-preS1) peptide domain of its large surface protein to NTCP. Since binding of the myr-preS1 peptide to NTCP is an initiating step of HBV infection, we investigated if this process interferes with the physiological bile acid transport function of NTCP.

METHODS

HBV infection, myr-preS1 peptide binding, and bile acid transport assays were performed with primary Tupaia belangeri (PTH) and human (PHH) hepatocytes as well as NTCP-transfected human hepatoma HepG2 cells allowing regulated NTCP expression, in the presence of various bile acids, ezetimibe, and myr-preS1 peptides.

RESULTS

The myr-preS1 peptide of HBV inhibited bile acid transport in PTH and PHH as well as in NTCP-expressing HEK293 and HepG2 cells. Inversely, HBV infection of PTH, PHH, and NTCP-transfected HepG2 cells was inhibited in a concentration-dependent manner by taurine and glycine conjugates of cholic acid and ursodeoxycholic acid as well as by ezetimibe. In NTCP-HepG2 cells and PTH, NTCP expression, NTCP transport function, myr-preS1 peptide binding, and HBV infection followed comparable kinetics.

CONCLUSIONS

Myr-preS1 virus binding to NTCP, necessary for productive HBV infection, interferes with the physiological bile acid transport function of NTCP. Therefore, HBV infection via NTCP may be lockable by NTCP substrates and NTCP-inhibiting drugs. This opens a completely new way for an efficient management of HBV infection by the use of NTCP-directed drugs.

Molecular mechanisms of ursodeoxycholic acid toxicity & side effects: ursodeoxycholic acid freezes regeneration & induces hibernation mode

Ursodeoxycholic acid (UDCA) is a steroid bile acid approved for primary biliary cirrhosis (PBC). UDCA is reported to have “hepato-protective properties”. Yet, UDCA has “unanticipated” toxicity, pronounced by more than double number of deaths, and eligibility for liver transplantation compared to the control group in 28 mg/kg/day in primary sclerosing cholangitis, necessitating trial halt in North America. UDCA is associated with increase in hepatocellular carcinoma in PBC especially when it fails to achieve biochemical response (10 and 15 years incidence of 9% and 20% respectively). “Unanticipated” UDCA toxicity includes hepatitis, pruritus, cholangitis, ascites, vanishing bile duct syndrome, liver cell failure, death, severe watery diarrhea, pneumonia, dysuria, immune-suppression, mutagenic effects and withdrawal syndrome upon sudden halt. UDCA inhibits DNA repair, co-enzyme A, cyclic AMP, p53, phagocytosis, and inhibits induction of nitric oxide synthatase. It is genotoxic, exerts aneugenic activity, and arrests apoptosis even after cellular phosphatidylserine externalization. UDCA toxicity is related to its interference with drug detoxification, being hydrophilic and anti-apoptotic, has a long half-life, has transcriptional mutational abilities, down-regulates cellular functions, has a very narrow difference between the recommended (13 mg/kg/day) and toxic dose (28 mg/kg/day), and it typically transforms into lithocholic acid that induces DNA strand breakage, it is uniquely co-mutagenic, and promotes cell transformation. UDCA beyond PBC is unjustified.

Bile acids for primary sclerosing cholangitis

BACKGROUND

Primary sclerosing cholangitis is a progressive chronic cholestatic liver disease that usually leads to the development of cirrhosis. Studies evaluating bile acids in the treatment of primary sclerosing cholangitis have shown a potential benefit of their use. However, no influence on patients survival and disease outcome has yet been proven.

OBJECTIVES

To assess the beneficial and harmful effects of bile acids for patients with primary sclerosing cholangitis.

SEARCH STRATEGY

We searched The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Library, MEDLINE, EMBASE and Science Citation Index Expanded generally from inception through to October 2010.

SELECTION CRITERIA

Randomised clinical trials comparing any dose of bile acids or duration of treatment versus placebo, no intervention, or another intervention were included irrespective of blinding, language, or publication status.

DATA COLLECTION AND ANALYSIS

Two authors extracted data independently. We evaluated the risk of bias of the trials using prespecified domains. We performed the meta-analysis according to the intention-to-treat principle. We presented outcomes as relative risks (RR) or mean differences (MD), both with 95% confidence intervals (CI).

MAIN RESULTS

Eight trials evaluated ursodeoxycholic acid versus placebo or no intervention (592 patients). The eight randomised clinical trials have a high risk of bias. Patients were treated for three months to six years (median three years). The dosage of ursodeoxycholic acid used in the trials ranged from low (10 mg/kg body weight/day) to high (28 to 30 mg/kg body weight/day). Ursodeoxycholic acid did not significantly reduce the risk of death (RR 1.00; 95% CI 0.46 to 2.20); treatment failure including liver transplantation, varices, ascites, and encephalopathy (RR 1.22; 95% CI 0.91 to 1.64); liver histological deterioration (RR 0.89; 95% CI 0.45 to 1.74); or liver cholangiographic deterioration (RR 0.60; 95% CI 0.23 to 1.57). Ursodeoxycholic acid significantly improved serum bilirubin (MD -14.6 µmol/litre; 95% CI -18.7 to -10.6), alkaline phosphatases (MD -506 IU/litre; 95% CI -583 to -430), aspartate aminotransferase (MD -46 IU/litre; 95% CI -77 to -16), and gamma-glutamyltranspeptidase (MD -260 IU/litre; 95% CI -315 to -205), but not albumin (MD -0.20 g/litre; 95% CI -1.91 to 1.50). Ursodeoxycholic acid was safe and well tolerated by patients with primary sclerosing cholangitis.

AUTHORS' CONCLUSIONS

We did not find enough evidence to support or refute the use of bile acids in the treatment of primary sclerosing cholangitis. However, bile acids seem to lead to a significant improvement in liver biochemistry. Therefore, more randomised trials are needed before any of the bile acids can be recommended for this indication.

Bile acids for liver-transplanted patients

BACKGROUND

Liver transplantation has become a widely accepted form of treatment for numerous end-stage liver diseases. Bile acids may decrease allograft rejection after liver transplantation by changing the expression of major histocompatibility complex class molecules in bile duct epithelium and central vein endothelium.

OBJECTIVES

To assess the beneficial and harmful effects of bile acids for liver-transplanted patients.

SEARCH STRATEGY

We performed searches of The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Central Register of Controlled Trials in The Cochrane Library, MEDLINE, EMBASE, and Science Citation Expanded to September, 2009.

SELECTION CRITERIA

Randomised clinical trials comparing any dose of bile acids or duration of treatment in liver-transplanted patients versus placebo, no intervention, or another intervention. We included randomised clinical trials irrespective of blinding, language, and publication status.

DATA COLLECTION AND ANALYSIS

Two review authors extracted and checked data independently. We evaluated the risk of bias of the trials from the method of allocation sequence generation, allocation concealment, blinding, outcome data analysis, outcome data reporting, and other potential sources of bias. We used the intention-to-treat principle to perform meta-analyses and presented the outcomes as relative risks (RR) or mean differences (MD), both with 95% confidence intervals (CI).

MAIN RESULTS

The updated search resulted in no new trials meeting the inclusion criteria of this review, thus leaving it to the seven already included randomised trials (six evaluating ursodeoxycholic acid versus placebo or no intervention, and one evaluating tauro-ursodeoxycholic acid versus no intervention) enrolling a total of 335 participants. The administration of bile acids began one day or more after liver transplantation. All patients received the standard triple-drug immunosuppressive regimen (steroids, azathioprine, and cyclosporine or tacrolimus) to suppress the allograft rejection response after liver transplantation. Bile acids compared with placebo or no intervention did not significantly change all-cause mortality (RR 0.85, 95% CI 0.53 to 1.36), mortality related to allograft rejection (RR 0.30, 95% CI 0.01 to 7.12), retransplantation (RR 0.76, 95% CI 0.20 to 2.86), acute cellular rejection, or number of patients with steroid-resistant rejection. Bile acids significantly reduced the number of patients who had chronic rejection in a fixed-effect model but not in a random-effects model meta-analysis. Bile acids were safe and well tolerated by liver-transplanted patients. However, this observation is based on data analysis from three trials with only 187 patients.

AUTHORS' CONCLUSIONS

We did not find evidence to support or refute bile acids for liver-transplanted patients. Further randomised trials are necessary before bile acids can be recommended to liver-transplanted patients.

Transactivation of the hepatitis B virus core promoter by the nuclear receptor FXRalpha

Hepatitis B virus (HBV) core promoter activity is positively and negatively regulated by nuclear receptors, a superfamily of ligand-activated transcription factors, via cis-acting sequences located in the viral genome. In this study, we investigated the role of farnesoid X receptor alpha (FXRalpha) in modulating transcription from the HBV core promoter. FXRalpha is a liver-enriched nuclear receptor activated by bile acids recognizing hormone response elements by forming heterodimers with retinoid X receptor alpha (RXRalpha). Electrophoretic mobility shift assays demonstrated that FXRalpha-RXRalpha heterodimers can bind two motifs on the HBV enhancer II and core promoter regions, presenting high homology to the consensus (AGGTCA) inverted repeat FXRalpha response elements. In transient transfection of the human hepatoma cell line Huh-7, bile acids enhanced the activity of a luciferase reporter containing the HBV enhancer II and core promoter sequences through FXRalpha. Moreover, using a greater-than-genome-length HBV construct, we showed that FXRalpha also increased synthesis of the viral pregenomic RNA and DNA replication intermediates. The data strongly suggest that FXRalpha is another member of the nuclear receptor superfamily implicated in the regulation of HBV core promoter activity and that bile acids could play an important role in the natural history of HBV infection.