Advances and Challenges in Studying Hepatitis B Virus In Vitro

Establishment and Characterization of an HBV Viral Spread and Infectious System following Long-Term Passage of an HBV Clinical Isolate in the Primary Human Hepatocyte and Fibroblast Coculture System

The existing cell culture-based methods to study hepatitis B virus (HBV) have limitations and do not allow for viral long-term passage. The aim of this study was to develop a robust in vitro long-term viral passage system with optimized cell culture conditions and a viral isolate with the ability to spread and passage. An HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized primary human hepatocyte (PHH)/human fibroblast coculture system. The passaged UV-treated virus was sequenced and further characterized. In addition, a panel of mutant viruses containing different combinations of mutations observed in this virus was investigated. The clinical isolate was passaged for 20 rounds with 21 days per round in an optimized PHH/human fibroblast coculture system while subject to UV mutagenesis. This passaged UV-mutated isolate harbored four mutations: G225A (sR24K) in the S gene, A2062T in the core gene, and two mutations G1764A and C1766T (xV131I) in the basal core promoter (BCP) region. In vitro characterization of the four mutations suggested that the two BCP mutations G1764A and C1766T contributed to the increased viral replication and viral infectivity. A robust in vitro long-term HBV viral passage system has been established by passaging a UV-treated clinical isolate in an optimized PHH/fibroblast coculture system. The two BCP mutations played a key role in the virus's ability to passage. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization. IMPORTANCE The existing cell culture-based methods to study HBV have limitations and do not allow for viral long-term passage. In this study, an HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized PHH/human fibroblast coculture system. This passaged UV-mutated isolate carried four mutations across the HBV genome, and in vitro characterization of the four mutations suggested that the two basal core promoter (BCP) mutations G1764A and C1766T played a key role in the virus's ability to passage. In summary, we have developed a robust in vitro long-term HBV viral passage system by passaging an UV-treated HBV genotype A clinical isolate in an optimized PHH/human fibroblast coculture system. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization.

Capsid Allosteric Modulators Enhance the Innate Immune Response in Hepatitis B Virus-Infected Hepatocytes During Interferon Administration

Capsid allosteric modulators (CAMs) inhibit the encapsidation of hepatitis B virus (HBV) pregenomic RNA (pgRNA), which contains a pathogen-associated molecular pattern motif. However, the effect of CAMs on the innate immune response of HBV-infected hepatocytes remains unclear, and we examined this effect in this study. Administration of a CAM compound, BAY41-4109 (BAY41), to HBV-infected primary human hepatocytes (PHHs) did not change the total cytoplasmic pgRNA levels but significantly reduced intracapsid pgRNA levels, suggesting that BAY41 increased extracapsid pgRNA levels in the cytoplasm. BAY41 alone did not change the intracellular interferon (IFN)-stimulated gene (ISG) expression levels. However, BAY41 enhanced antiviral ISG induction by IFN-α in HBV-infected PHHs but did not change ISG induction by IFN-α in uninfected PHHs. Compared with BAY41 or IFN-α alone, coadministration of BAY41 and IFN-α significantly suppressed extracellular HBV-DNA levels. HBV-infected human liver-chimeric mice were treated with vehicle, BAY41, pegylated IFN-α (pegIFN-α), or BAY41 and pegIFN-α together. Compared with the vehicle control, pegIFN-α highly up-regulated intrahepatic ISG expression levels, but BAY41 alone did not change these levels. The combination of BAY41 and pegIFN-α further enhanced intrahepatic antiviral ISG expression, which was up-regulated by pegIFNα. The serum HBV-DNA levels in mice treated with the combination of BAY41 and pegIFN-α were the lowest observed in all the groups. Conclusion: CAMs enhance the host IFN response when combined with exogenous IFN-α, likely due to increased cytoplasmic extracapsid pgRNA.

Metabolically Improved Stem Cell Derived Hepatocyte-Like Cells Support HBV Life Cycle and Are a Promising Tool for HBV Studies and Antiviral Drug Screenings

More than 300 million people worldwide are diagnosed with a chronic hepatitis B virus (HBV) infection. Nucleos(t)ide viral polymerase inhibitors are available on the market and can efficiently treat patients with chronic HBV. However, life-long treatment is needed as covalently closed circular DNA (cccDNA) persists in the hepatocyte nucleus. Hence, there is a high demand for novel therapeutics that can eliminate cccDNA from the hepatocyte nucleus and cure chronically infected HBV patients. The gold standard for in vitro HBV studies is primary human hepatocytes (PHHs). However, alternatives are needed due to donor organ shortage and high batch-to-batch variability. Therefore, human pluripotent stem cell (hPSC)-derived hepatocyte-like cells (HLCs) are being explored as an in vitro HBV infection model. We recently generated hPSC lines that overexpress three transcription factors (HC3x) and that, upon differentiation in a high amino-acid supplemented maturation medium, generate a more mature hepatocyte progeny (HC3x-AA-HLCs). Here, we demonstrate that HBV can efficiently infect these HC3x-AA-HLCs, as was shown by the presence of HBV core (HBc) and surface antigens. A clear increasing release of HBV surface and e antigens was detected, indicating the formation of functional cccDNA. Moreover, back-titration of culture supernatant of HBV-infected HC3x-AA-HLCs on HepG2-NTCP cells revealed the production of novel infectious HBV particles. Additionally, an increasing number of HBc-positive HC3x-AA-HLCs over time suggests viral spreading is occurring. Finally, the HC3x-AA-HLC model was validated for use in antiviral drug studies using the nucleoside reverse-transcriptase inhibitor, lamivudine, and the HBV entry inhibitor, Myrcludex B.

Hepatitis B virus infection modeling using multi-cellular organoids derived from human induced pluripotent stem cells

Chronic infection with hepatitis B virus (HBV) remains a global health concern despite the availability of vaccines. To date, the development of effective treatments has been severely hampered by the lack of reliable, reproducible, and scalable in vitro modeling systems that precisely recapitulate the virus life cycle and represent virus-host interactions. With the progressive understanding of liver organogenesis mechanisms, the development of human induced pluripotent stem cell (iPSC)-derived hepatic sources and stromal cellular compositions provides novel strategies for personalized modeling and treatment of liver disease. Further, advancements in three-dimensional culture of self-organized liver-like organoids considerably promote in vitro modeling of intact human liver tissue, in terms of both hepatic function and other physiological characteristics. Combined with our experiences in the investigation of HBV infections using liver organoids, we have summarized the advances in modeling reported thus far and discussed the limitations and ongoing challenges in the application of liver organoids, particularly those with multi-cellular components derived from human iPSCs. This review provides general guidelines for establishing clinical-grade iPSC-derived multi-cellular organoids in modeling personalized hepatitis virus infection and other liver diseases, as well as drug testing and transplantation therapy.

Cell Culture Models for the Study of Hepatitis D Virus Entry and Infection

Chronic hepatitis D is one of the most severe and aggressive forms of chronic viral hepatitis with a high risk of developing hepatocellular carcinoma (HCC). It results from the co-infection of the liver with the hepatitis B virus (HBV) and its satellite, the hepatitis D virus (HDV). Although current therapies can control HBV infection, no treatment that efficiently eliminates HDV is available and novel therapeutic strategies are needed. Although the HDV cycle is well described, the lack of simple experimental models has restricted the study of host–virus interactions, even if they represent relevant therapeutic targets. In the last few years, the discovery of the sodium taurocholate co-transporting polypeptide (NTCP) as a key cellular entry factor for HBV and HDV has allowed the development of new cell culture models susceptible to HBV and HDV infection. In this review, we summarize the main in vitro model systems used for the study of HDV entry and infection, discuss their benefits and limitations and highlight perspectives for future developments.

Bioengineered Liver Models for Investigating Disease Pathogenesis and Regenerative Medicine

Owing to species-specific differences in liver pathways, in vitro human liver models are utilized for elucidating mechanisms underlying disease pathogenesis, drug development, and regenerative medicine. To mitigate limitations with de-differentiated cultures, bioengineers have developed advanced techniques/platforms, including micropatterned cocultures, spheroids/organoids, bioprinting, and microfluidic devices, for perfusing cell cultures and liver slices. Such techniques improve mature functions and culture lifetime of primary and stem-cell human liver cells. Furthermore, bioengineered liver models display several features of liver diseases including infections with pathogens (e.g., malaria, hepatitis C/B viruses, Zika, dengue, yellow fever), alcoholic/nonalcoholic fatty liver disease, and cancer. Here, we discuss features of bioengineered human liver models, their uses for modeling aforementioned diseases, and how such models are being augmented/adapted for fabricating implantable human liver tissues for clinical therapy. Ultimately, continued advances in bioengineered human liver models have the potential to aid the development of novel, safe, and efficacious therapies for liver disease.

Cross talk between hepatitis B virus and innate immunity of hepatocytes

Innate immunity plays a major role in controlling viral infections. Recent exploration of sodium taurocholate co-transporting polypeptide receptor as specific hepatitis B virus (HBV) receptor in human hepatocytes has provided appropriate cell culture tools to study the innate immunity of hepatocytes and its cross talk with HBV. In this review, we give a brief update on interaction between HBV and innate immunity using the currently available in vitro cellular models that support the complete life cycle of HBV. We will discuss how HBV can act as a 'stealth' virus to counteract the innate immune responses mediated by the pathogen recognition receptors of hepatocytes and escape the first line of surveillance of the host immune system. We give an overview of the cellular components of innate immunity that present in these in vitro models and discuss how activating these innate immunity components may contribute to the eradication of HBV infection.

Bioengineered Liver Cell Models of Hepatotropic Infections

Hepatitis viruses and liver-stage malaria are within the liver infections causing higher morbidity and mortality rates worldwide. The highly restricted tropism of the major human hepatotropic pathogens-namely, the human hepatitis B and C viruses and the Plasmodium falciparum and Plasmodium vivax parasites-has hampered the development of disease models. These models are crucial for uncovering the molecular mechanisms underlying the biology of infection and governing host-pathogen interaction, as well as for fostering drug development. Bioengineered cell models better recapitulate the human liver microenvironment and extend hepatocyte viability and phenotype in vitro, when compared with conventional two-dimensional cell models. In this article, we review the bioengineering tools employed in the development of hepatic cell models for studying infection, with an emphasis on 3D cell culture strategies, and discuss how those tools contributed to the level of recapitulation attained in the different model layouts. Examples of host-pathogen interactions uncovered by engineered liver models and their usefulness in drug development are also presented. Finally, we address the current bottlenecks, trends, and prospect toward cell models' reliability, robustness, and reproducibility.

In Vitro Infection with Hepatitis B Virus Using Differentiated Human Serum Culture of Huh7.5-NTCP Cells without Requiring Dimethyl Sulfoxide

An estimated two billion people worldwide have been infected with hepatitis B virus (HBV). Despite the high infectivity of HBV in vivo, a lack of easily infectable in vitro culture systems hinders studies of HBV. Overexpression of the sodium taurocholate co-transporting polypeptide (NTCP) bile acid transporter in hepatoma cells improved infection efficiency. We report here a hepatoma cell culture system that does not require dimethyl sulfoxide (DMSO) for HBV infection. We overexpressed NTCP in Huh7.5 cells and allowed these cells to differentiate in a medium supplemented with human serum (HS) instead of fetal bovine serum (FBS). We show that human serum culture enhanced HBV infection in Huh7.5-NTCP cells, e.g., in HS cultures, HBV pgRNA levels were increased by as much as 200-fold in comparison with FBS cultures and 19-fold in comparison with FBS+DMSO cultures. Human serum culture increased levels of hepatocyte differentiation markers, such as albumin secretion, in Huh7.5-NTCP cells to similar levels found in primary human hepatocytes. N-glycosylation of NTCP induced by culture in human serum may contribute to viral entry. Our study demonstrates an in vitro HBV infection of Huh7.5-NTCP cells without the use of potentially toxic DMSO.

Immortalized stem cell-derived hepatocyte-like cells: An alternative model for studying dengue pathogenesis and therapy

Suitable cell models are essential to advance our understanding of the pathogenesis of liver diseases and the development of therapeutic strategies. Primary human hepatocytes (PHHs), the most ideal hepatic model, are commercially available, but they are expensive and vary from lot-to-lot which confounds their utility. We have recently developed an immortalized hepatocyte-like cell line (imHC) from human mesenchymal stem cells, and tested it for use as a substitute model for hepatotropic infectious diseases. With a special interest in liver pathogenesis of viral infection, herein we determined the suitability of imHC as a host cell target for dengue virus (DENV) and as a model for anti-viral drug testing. We characterized the kinetics of DENV production, cellular responses to DENV infection (apoptosis, cytokine production and lipid droplet metabolism), and examined anti-viral drug effects in imHC cells with comparisons to the commonly used hepatoma cell lines (HepG2 and Huh-7) and PHHs. Our results showed that imHC cells had higher efficiencies in DENV replication and NS1 secretion as compared to HepG2 and Huh-7 cells. The kinetics of DENV infection in imHC cells showed a slower rate of apoptosis than the hepatoma cell lines and a certain similarity of cytokine profiles to PHHs. In imHC, DENV-induced alterations in levels of lipid droplets and triacylglycerols, a major component of lipid droplets, were more apparent than in hepatoma cell lines, suggesting active lipid metabolism in imHC. Significantly, responses to drugs with DENV inhibitory effects were greater in imHC cells than in HepG2 and Huh-7 cells. In conclusion, our findings suggest superior suitability of imHC as a new hepatocyte model for studying mechanisms underlying viral pathogenesis, liver diseases and drug effects.

A model system resembling normal human liver cells is needed for advancement of hepatotropic infectious disease research. Here we show that immortalized cells (imHC) derived from human stem cells have a higher efficiency of DENV replication and a lower rate of cell death in response to DENV infection than the cancer cell-derived model systems currently used. The imHC also have active fat metabolism and respond well to anti-viral drug treatment, making them an attractive model for the initial stage of drug discovery and testing.

EGF receptor inhibitors comprehensively suppress hepatitis B virus by downregulation of STAT3 phosphorylation

Current antiviral therapy can not cure chronic hepatitis B virus (HBV) infection or eliminate the risk of hepatocellular carcinoma. The licensed epidermal growth factor receptor (EGFR) inhibitors have found to inhibit hepatitis C virus replication via downregulation of signal transducers and activators of transcription 3 (STAT3) phosphorylation. Since STAT3 is also involved in HBV replication, we further studied the anti-HBV efficacy of the EGFR inhibitors in this study. HBV-transfected HepG2.2.15 cells and HBV-infected HepG2-NTCP cells were used as cell models, and HBV replication, the syntheses of viral antigens and the magnitude of the covalently closed circular DNA (cccDNA) reservoir were used as indictors to test the anti-HBV effects of EGFR inhibitors erlotinib and gefitinib. Erlotinib inhibited HBV replication with a half-maximal inhibitory concentration of 1.05 μM. It also reduced the syntheses of viral antigens at concentrations of 2.5 μM or higher. The underlying mechanism was possibly correlated with its inhibition on STAT3 phosphorylation via up-regulation of suppressor of cytokine signaling 3. Gefitinib also inhibited HBV replication and antigen syntheses. Compared with the commonest antiviral drug entecavir, these EGFR inhibitors additionally reduced hepatitis B e antigen and erlotinib also marginally affected the cccDNA reservoir in HBV-infected HepG2-NTCP cells. Interestingly, these promising anti-HBV effects were significantly enhanced by extension of treatment duration. In conclusion, EGFR inhibitors demonstrated a comprehensive anti-HBV potential, highlighting a new strategy to cure HBV infection and suggesting animal model-related studies or clinical try in the future.

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We test the anti-HBV potential of EGFR inhibitors erlotinib and gefitinib in vitro.

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Erlotinib inhibits HBV replication in clinically safe concentrations.

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EGFR inhibitors suppress HBV by downregulation of STAT3 phosphorylation.

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EGFR inhibitors show a comprehensive anti-HBV potential including the cccDNA.

In Vitro Systems for Studying Different Genotypes/Sub-Genotypes of Hepatitis B Virus: Strengths and Limitations

Hepatitis B virus (HBV) infects the liver resulting in end stage liver disease, cirrhosis, and hepatocellular carcinoma. Despite an effective vaccine, HBV poses a serious health problem globally, accounting for 257 million chronic carriers. Unique features of HBV, including its narrow virus-host range and its hepatocyte tropism, have led to major challenges in the development of suitable in vivo and in vitro model systems to recapitulate the HBV replication cycle and to test various antiviral strategies. Moreover, HBV is classified into at least nine genotypes and 35 sub-genotypes with distinct geographical distributions and prevalence, which have different natural histories of infection, clinical manifestation, and response to current antiviral agents. Here, we review various in vitro systems used to study the molecular biology of the different (sub)genotypes of HBV and their response to antiviral agents, and we discuss their strengths and limitations. Despite the advances made, no system is ideal for pan-genotypic HBV research or drug development and therefore further improvement is required. It is necessary to establish a centralized repository of HBV-related generated materials, which are readily accessible to HBV researchers, with international collaboration toward advancement and development of in vitro model systems for testing new HBV antivirals to ensure their pan-genotypic and/or customized activity.

Emerging trends in modeling human liver disease in vitro

The liver executes 500+ functions, such as protein synthesis, xenobiotic metabolism, bile production, and metabolism of carbohydrates/fats/proteins. Such functions can be severely degraded by drug-induced liver injury, nonalcoholic fatty liver disease, hepatitis B and viral infections, and hepatocellular carcinoma. These liver diseases, which represent a significant global health burden, are the subject of novel drug discovery by the pharmaceutical industry via the use of in vitro models of the human liver, given significant species-specific differences in disease profiles and drug outcomes. Isolated primary human hepatocytes (PHHs) are a physiologically relevant cell source to construct such models; however, these cells display a rapid decline in the phenotypic function within conventional 2-dimensional monocultures. To address such a limitation, several engineered platforms have been developed such as high-throughput cellular microarrays, micropatterned cocultures, self-assembled spheroids, bioprinted tissues, and perfusion devices; many of these platforms are being used to coculture PHHs with liver nonparenchymal cells to model complex cell cross talk in liver pathophysiology. In this perspective, we focus on the utility of representative platforms for mimicking key features of liver dysfunction in the context of chronic liver diseases and liver cancer. We further discuss pending issues that will need to be addressed in this field moving forward. Collectively, these in vitro liver disease models are being increasingly applied toward the development of new therapeutics that display an optimal balance of safety and efficacy, with a focus on expediting development, reducing high costs, and preventing harm to patients.

Comprehensive Proteomics Identification of IFN-λ3-regulated Antiviral Proteins in HBV-transfected Cells

Interferon lambda (IFN-λ) is a relatively unexplored, yet promising antiviral agent. IFN-λ has recently been tested in clinical trials of chronic hepatitis B virus infection (CHB), with the advantage that side effects may be limited compared with IFN-α, as IFN-λ receptors are found only in epithelial cells. To date, IFN-λ's downstream signaling pathway remains largely unelucidated, particularly via proteomics methods. Here, we report that IFN-λ3 inhibits HBV replication in HepG2.2.15 cells, reducing levels of both HBV transcripts and intracellular HBV DNA. Quantitative proteomic analysis of HBV-transfected cells was performed following 24-hour IFN-λ3 treatment, with parallel IFN-α2a and PBS treatments for comparison using a dimethyl labeling method. The depth of the study allowed us to map the induction of antiviral proteins to multiple points of the viral life cycle, as well as facilitating the identification of antiviral proteins not previously known to be elicited upon HBV infection (e.g. IFITM3, XRN2, and NT5C3A). This study also shows up-regulation of many effectors involved in antigen processing/presentation indicating that this cytokine exerted immunomodulatory effects through several essential molecules for these processes. Interestingly, the 2 subunits of the immunoproteasome cap (PSME1 and PSME2) were up-regulated whereas cap components of the constitutive proteasome were down-regulated upon both IFN treatments, suggesting coordinated modulation toward the antigen processing/presentation mode. Furthermore, in addition to confirming canonical activation of interferon-stimulated gene (ISG) transcription through the JAK-STAT pathway, we reveal that IFN-λ3 restored levels of RIG-I and RIG-G, proteins known to be suppressed by HBV. Enrichment analysis demonstrated that several biological processes including RNA metabolism, translation, and ER-targeting were differentially regulated upon treatment with IFN-λ3 versus IFN-α2a. Our proteomic data suggests that IFN-λ3 regulates an array of cellular processes to control HBV replication.

Sleeping Beauty Transposon-based System forRapid Generation of HBV-replicating Stable Cell Lines

The stable HBV-transfected cell lines, which based on stable integration of replication-competent HBV genome into hepatic cells, are widely used in basic research and antiviral drug evaluation against HBV. However, previous reported strategies to generate HBV-replicating cell lines, which primarily rely on random integration of exogenous DNA by plasmid transfection, are inefficient and time-consuming. We newly developed an all-in-one Sleeping Beauty transposon system (denoted pTSMP-HBV vector) for robust generation of stable HBV-replicating cell lines of different genotype. The pTSMP-HBV vector contains HBV 1.3-copy genome and dual selection markers (mCherry and puromycin resistance gene), allowing rapid enrichment of stably-transfected cells via red fluorescence-activated cell sorting and puromycin antibiotic selection. In this protocol, we described the detailed procedure for constructing the HBV-replicating stable cells and systematically evaluating HBV replication and viral protein expression profiles of these cells.

Characterization of the hepatitis B virus DNA detected in urine of chronic hepatitis B patients

Background

Detection of human hepatitis B virus (HBV) DNA in the urine of patients with chronic hepatitis B infection (CHB) has been reported previously, suggesting urine could provide a potential route of horizontal HBV transmission. However, it is not clear whether the HBV DNA detected in urine is indeed full-length, infectious viral DNA. The aim of this study is to assess the potential infectivity of urine from patients with CHB and to correlate HBV DNA detection in urine with clinical parameters, such as serum viral load and HBeAg status.

Methods

Urine from 60 CHB patients with serum viral loads ranging from undetectable to 10⁸ IU/mL were analyzed for HBV DNA and serum immune markers. HBV DNA was detected from total urine DNA and size-fractionated urine DNA (separated into ≤1 kb and > 1 kb fractions) by PCR analysis of six regions of the HBV genome.

Results

Twenty-seven of 59 (45.7%) patients with HBV serum viral load (≥20 IU/mL) contained at least 20 copies per mL of fragmented HBV DNA in urine detected in at least 1 of the 6 PCR assay regions. Only one patient contained HBV DNA detected by all six regions, and was found to have evidence of blood in the urine. Sixteen of 25 urine samples with high viral load (> 10⁵ IU/mL) and 11 of 34 urine samples with low viral load (< 10⁵ IU/mL) contained detectable HBV DNA. Twelve of 27 (44.44%) patients with detectable HBV DNA in urine were HBeAg positive, and only 5 of these HBeAg positive patients were in the group of 33 (15.15%) patients with no detectable HBV DNA in urine. By Fishers’ exact test, HBV DNA in urine is significantly associated with high serum viral load (P = 0.0197) and HBeAg (P = 0.0203).

Conclusions

We conclude that urine from CHB patients with healthy kidney function should not contain full-length HBV DNA, and therefore should not be infectious.

Electronic supplementary material

The online version of this article (10.1186/s12876-018-0767-1) contains supplementary material, which is available to authorized users.

Simultaneous Assessment of Clearance, Metabolism, Induction, and Drug-Drug Interaction Potential Using a Long-Term In Vitro Liver Model for a Novel Hepatitis B Virus Inhibitor

Long-term in vitro liver models are now widely explored for human hepatic metabolic clearance prediction, enzyme phenotyping, cross-species metabolism, comparison of low clearance drugs, and induction studies. Here, we present studies using a long-term liver model, which show how metabolism and active transport, drug-drug interactions, and enzyme induction in healthy and diseased states, such as hepatitis B virus (HBV) infection, may be assessed in a single test system to enable effective data integration for physiologically based pharmacokinetic (PBPK) modeling. The approach is exemplified in the case of (3S)-4-[[(4R)-4-(2-Chloro-4-fluorophenyl)-5-methoxycarbonyl-2-thiazol-2-yl-1,4-dihydropyrimidin-6-yl]methyl]morpholine-3-carboxylic acid RO6889678, a novel inhibitor of HBV with a complex absorption, distribution, metabolism, and excretion (ADME) profile. RO6889678 showed an intracellular enrichment of 78-fold in hepatocytes, with an apparent intrinsic clearance of 5.2 µl/min per mg protein and uptake and biliary clearances of 2.6 and 1.6 µl/min per mg protein, respectively. When apparent intrinsic clearance was incorporated into a PBPK model, the simulated oral human profiles were in good agreement with observed data at low doses but were underestimated at high doses due to unexpected overproportional increases in exposure with dose. In addition, the induction potential of RO6889678 on cytochrome P450 (P450) enzymes and transporters at steady state was assessed and cotreatment with ritonavir revealed a complex drug-drug interaction with concurrent P450 inhibition and moderate UDP-glucuronosyltransferase induction. Furthermore, we report on the first evaluation of in vitro pharmacokinetics studies using HBV-infected HepatoPac cocultures. Thus, long-term liver models have great potential as translational research tools exploring pharmacokinetics of novel drugs in vitro in health and disease.

Bile acids induce necrosis in pancreatic stellate cells dependent on calcium entry and sodium-driven bile uptake

KEY POINTS

Acute biliary pancreatitis is a sudden and severe condition initiated by bile reflux into the pancreas. Bile acids are known to induce Ca2+ signals and necrosis in isolated pancreatic acinar cells but the effects of bile acids on stellate cells are unexplored. Here we show that cholate and taurocholate elicit more dramatic Ca2+ signals and necrosis in stellate cells compared to the adjacent acinar cells in pancreatic lobules; whereas taurolithocholic acid 3-sulfate primarily affects acinar cells. Ca2+ signals and necrosis are strongly dependent on extracellular Ca2+ as well as Na+ ; and Na+ -dependent transport plays an important role in the overall bile acid uptake in pancreatic stellate cells. Bile acid-mediated pancreatic damage can be further escalated by bradykinin-induced signals in stellate cells and thus killing of stellate cells by bile acids might have important implications in acute biliary pancreatitis.

ABSTRACT

Acute biliary pancreatitis, caused by bile reflux into the pancreas, is a serious condition characterised by premature activation of digestive enzymes within acinar cells, followed by necrosis and inflammation. Bile acids are known to induce pathological Ca2+ signals and necrosis in acinar cells. However, bile acid-elicited signalling events in stellate cells remain unexplored. This is the first study to demonstrate the pathophysiological effects of bile acids on stellate cells in two experimental models: ex vivo (mouse pancreatic lobules) and in vitro (human cells). Sodium cholate and taurocholate induced cytosolic Ca2+ elevations in stellate cells, larger than those elicited simultaneously in the neighbouring acinar cells. In contrast, taurolithocholic acid 3-sulfate (TLC-S), known to induce Ca2+ oscillations in acinar cells, had only minor effects on stellate cells in lobules. The dependence of the Ca2+ signals on extracellular Na+ and the presence of sodium-taurocholate cotransporting polypeptide (NTCP) indicate a Na+ -dependent bile acid uptake mechanism in stellate cells. Bile acid treatment caused necrosis predominantly in stellate cells, which was abolished by removal of extracellular Ca2+ and significantly reduced in the absence of Na+ , showing that bile-dependent cell death was a downstream event of Ca2+ signals. Finally, combined application of TLC-S and the inflammatory mediator bradykinin caused more extensive necrosis in both stellate and acinar cells than TLC-S alone. Our findings shed new light on the mechanism by which bile acids promote pancreatic pathology. This involves not only signalling in acinar cells but also in stellate cells.

Screening of differentially expressed genes in chronic hepatitis B patients and prediction of related biological pathways

AIM: To study the molecular mechanism of pathogenesis of chronic hepatitis B.

METHODS: Based on microarray experiment, GeneSpring software was used to screen differentially expressed genes in chronic hepatitis B patients, and GeneTrail software was used to perform enrichment analysis of related biological pathways.

RESULTS: A total of 417 differentially expressed genes were identified, of which 205 were upregulated and 212 downregulated. Significant pathways to which downregulated genes belong include ErbB, non-small cell lung cancer, mTOR, RNA degradation, T cell receptor, chronic myeloid leukemia, and renal cell carcinoma pathways. Significant pathways to which upregulated genes belong include chemokine, lysosomes, Vibrio cholerae infection, and IgG Fc receptor-mediated phagocytosis pathways.

CONCLUSION: PI3K/AKT downregulation is likely a major molecular mechanism of persistent hepatitis B.