Extracellular matrix proteins modulate cytochrome P450 2D6 expression in human hepatocytes

Characterization of a liver organoid tissue composed of hepatocytes and fibroblasts in dense collagen fibrils

The adult liver is wrapped in a connective tissue sheet called the liver capsule, which consists of collagen fibrils and fibroblasts. In this study, we set out to construct a liver organoid tissue that would be comparable to the endogenous liver, using a bioreactor. In vitro liver organoid tissue was generated by combining collagen fibrils, fibroblasts, and primary murine hepatocytes or Hep G2 on a mesh of poly-lactic acid fabric using a bioreactor. Then, the suitability of this liver organoid tissue for transplantation was tested by implanting the constructs into partially hepatectomized BALB/cA-nu/nu mice. As determined by using scanning and transmission electron microscopes, the liver organoid tissues were composed of densely packed collagen fibrils with fibroblasts and aggregates of oval or spherical hepatocytes. Angiogenesis was induced after the transplantation, and blood vessels connected the liver organoid tissue with the surrounding tissue. Thus, a novel approach was applied to generate transplantable liver organoid tissue within a condensed collagen fibril matrix. These results suggested that a dense collagen network populated with fibroblasts can hold a layer of concentrated hepatocytes, providing a three-dimensional microenvrionment suitable for the reestablishment of cell-cell and cell-extracellular matrix (ECM) interactions, and resulting in the maintenance of their liver-specific functions. This liver organoid tissue may be useful for the study of intrahepatic functions of various cells, cytokines, and ECMs, and may fulfill the fundamental requirements of a donor tissue.

Analysis of the core gene of hepatitis B virus in Korean patients

BACKGROUND/AIMS

As the core gene of hepatitis B virus (HBV) is a major immunological target, its mutation may evoke or evade immune clearance. We investigated the frequency and location of HBV core gene substitutions according to hepatitis B e antigen (HBeAg) status and viral replication status, and evaluated the association of these substitutions with the different stages of chronic HBV infection in Korean patients.

METHODS

The study population included 45 HBeAg-positive/DNA-positive patients (group I), 49 HBeAg-negative/DNA-positive patients (II) and 50 HBeAg-negative/DNA-negative patients (III). The HBV core gene was analysed by polymerase chain reaction (PCR) and sequencing.

RESULTS

The frequency of core gene substitutions increased from group I to group III. Substitutions were commonly detected at codons 87, 97, 112 and 130. The frequency of substitutions at codons 87 and 112 was higher in groups II/III than in group I. The frequency of the codon I97F substitutions was the highest in group III. However, the codon 130 substitution was more frequently found in groups I/II than in group III.

CONCLUSION

Core gene substitutions were more frequently detected in HBeAg-negative and/or HBV DNA-negative patients. The substitutional hot spots were codons 87, 97, 112 and 130; substitutions at these codons might play a role in immune-modulation during the course of chronic HBV infection.

Hot-spot mutations in hepatitis B virus core gene: eliciting or evading immune clearance?

The biological implications of substitutions L60V and I97L in the core (c) gene of hepatitis B virus (HBV) were investigated in order to determine whether they could change the immunogenicity of HBcAg or influence the immune response in mice. Three strains of recombinant adenoviruses--AdHBV-WT, AdHBV-L60V and AdHBV-I97L--containing wild-type or mutant HBV genomes were constructed using the AdEasy system and used to infect BALB/c mice intranasally. Infected mice produced anti-HBc efficiently to comparable levels. IgG1 and IgG2a specific for HBcAg were present in mice sera, and the response was dominated by IgG2a. The lymphocyte proliferative response specific for HBcAg was assessed by [3H]-thymidine uptake. We found that AdHBV-WT induced a stronger T-cell proliferation response than AdHBV-L60V and AdHBV-I97L. In conclusion, the L60V and I97L substitutions had no influence on humoral immune responses, but could downregulate T-cell responses to HBcAg, suggesting that L60V and I97L were immune escape mutants.

HBV core sequence: definition of genotype-specific variability and correlation with geographical origin

There are eight genotypes and nine subtypes of HBV. Small differences in geographical origin are associated with sequence changes in the surface gene. Here, we compared core gene sequences from different genotypes and geographical regions. Specific combinations of 24 amino acid substitutions at nine residues allowed allocation of a sequence to a subtype. Six of these nine residues were located in different T cell epitopes depending on HBV geographical area and/or genotype. Thirty-seven nucleotide changes were associated uniquely with specific genotypes and subtypes. Unique amino acid and nucleotide variants were found in a majority of sequences from specific countries as well as within subtype ayw2 and adr. Specific nucleotide motifs were defined for Korean, Indian, Chinese, Italian and Pacific region isolates. Finally, we observed amino acid motifs that were common to either South-east Asian or Western populations, irrespective of subtype. We believe that HBV strains spread within constrained ethnic groups, result in selection pressures that define sequence variability within each subtype. It suggests that particular T cell epitopes are specific for geographical regions, and thus ethnic groups; this may affect the design of immunomodulatory therapies.

Effects of prototypical microsomal enzyme inducers on cytochrome P450 expression in cultured human hepatocytes

Cultured human hepatocytes are a valuable in vitro system for evaluating new molecular entities as inducers of cytochrome P450 (P450) enzymes. The present study summarizes data obtained from 62 preparations of cultured human hepatocytes that were treated with vehicles (saline or dimethylsulfoxide, 0.1%), beta-naphthoflavone (33 microM), phenobarbital (100 or 250 microM), isoniazid (100 microM) and/or rifampin (20 or 50 microM), and examined for the expression of P450 enzymes based on microsomal activity toward marker substrates, or in the case of CYP2C8, the level of immunoreactive protein. The results show that CYP1A2 activity was markedly induced by beta-naphthoflavone (on average 13-fold, n = 28 preparations), and weakly induced by phenobarbital (1.9-fold, n = 25) and rifampin (2.3-fold, n = 22); CYP2A6 activity tended to be increased with phenobarbital (n = 7) and rifampin (n = 3) treatments, but the effects were not statistically significant; CYP2B6 was induced by phenobarbital (6.5-fold, n = 13) and rifampin (13-fold, n = 14); CYP2C8 was induced by phenobarbital (4.0-fold, n = 4) and rifampin (5.2-fold, n = 4); CYP2C9 was induced by phenobarbital (1.8-fold, n = 14) and rifampin (3.5-fold, n = 10); CYP2C19 was markedly induced by rifampin (37-fold, n = 10), but relatively modestly by phenobarbital (7-fold, n = 9); CYP2D6 was not significantly induced by phenobarbital (n = 5) or rifampin (n = 5); CYP2E1 was induced by phenobarbital (1.7-fold, n = 5), rifampin (2.2-fold, n = 5), and isoniazid (2.3-fold, n = 5); and, CYP3A4 was induced by phenobarbital (3.3-fold, n = 42) and rifampin (10-fold, n = 61), but not by beta-naphthoflavone. Based on these observations, we generalize that beta-naphthoflavone induces CYP1A2 and isoniazid induces CYP2E1, whereas rifampin and, to a lesser extent phenobarbital, tend to significantly and consistently induce enzymes of the CYP2A, CYP2B, CYP2C, CYP2E, and CYP3A subfamilies but not the 2D subfamily.

The role of surface wettability on hepatocyte adhesive interactions and function

In this paper the effect of surface wettability on hepatocyte morphology and function was studied, using clean and octadecylsylane (ODS)-coated glass as a model for hydrophilic and hydrophobic surfaces, respectively. C3A cells--a hepatoblastoma cell line, and freshly obtained porcine hepatocytes were cultured for a short-time period of up to 4 days on the above substrata. Hepatocyte adhesive interactions were characterized monitoring the initial cell attachment, the overall cell morphology, the formation of focal adhesions, and actin filaments. Since hepatocytes showed a clear tendency for homotypic adhesion on ODS, specific E-cadherin staining was used to visualize the intercellular contacts by immunofluorescence microscopy. Additionally, functional assays were carried out to monitor proliferation, metabolic activity, and albumin synthesis of C3A cells. It could be shown that both C3A cells and normal porcine hepatocytes spread better on hydrophilic glass; spreading being accompanied by the development of pronounced actin stress fibers and focal adhesion contacts. In contrast, on hydrophobic substrata predominant cell-cell interactions took place which led to intense E-cadherin staining in the intercellular contacts of porcine hepatocytes but not in C3A cells. On the other hand, metabolic activity and growth of C3A cells were reduced on hydrophobic ODS, but albumin synthesis was similar on both surfaces. It was concluded that the wettability of materials has a strong influence on the attachment and morphology of hepatocytes while the influence of surface properties on the functional activity of hepatocytes still remains to be elucidated.

Diagnosis and management of pre-core mutant chronic hepatitis B

Chronic hepatitis due to pre-core hepatitis B virus (HBV) mutants presents as hepatitis B e antigen (HBeAg)-negative chronic hepatitis B (CHB). HBeAg-negative CHB represents a late phase in the natural course of chronic HBV infection that develops after HBeAg loss and seroconversion to anti-HBe. It is usually associated with pre-core stop codon mutation at nucleotide 1896 (mainly selected in non-A HBV genotypes), but also with other pre-core changes or with mutations in the basic core promoter region (mainly in HBV genotype A). In chronic HBV infections, pre-core mutants can be detected both in patients with HBeAg-negative CHB and in inactive hepatitis B surface antigen (HBsAg) carriers. The diagnosis of HBeAg-negative CHB is based on HBsAg positivity, HBeAg negativity, and mainly on increased alanine aminotransferase (ALT) and serum HBV-DNA levels and exclusion of other causes of liver disease. The differential diagnosis between patients with CHB and inactive HBsAg carriers can be made only by close follow-up of aminotransferase activity and viraemia levels, although the cut-off level of serum HBV DNA has not been definitely determined. IgM anti-HBc levels have also been suggested as an index that increases the diagnostic accuracy for transient hepatitis flares, while liver biopsy confirms the diagnosis and evaluates the severity of the liver disease. Interferon-alpha (IFN-alpha) and lamivudine are the two drugs that have been tried, mainly in the management of HBeAg-negative CHB. A 12-month course of IFN-alpha achieves sustained biochemical remission in about 20% of patients, which has been associated with improvement in the long-term outcome of this subset. A 12-month course of lamivudine is rather ineffective, maintaining remission in less than 15% of patients after cessation of therapy. Long-term lamivudine is associated with progressively increasing rate of virological and subsequent biochemical breakthroughs due to YMDD mutants, with approximately 30% of patients remaining in remission in the third year of therapy. Several other antiviral agents are currently being evaluated in this setting with combined regimens being the most reasonable step for the near future.

Time-dependent expression of cytochrome P450 genes in primary cultures of well-differentiated human hepatocytes

We sought to establish an in vitro system to study the regulation of highly differentiated hepatocellular functions, and specifically the time-dependent expression of four cytochrome P450 (P450) genes at the messenger RNA (mRNA) and protein levels. When seeded onto matrigel, hepatocytes could be maintained for 8 days in media that were free of serum and hormones (except for insulin). Cells retained a spherical phenotype; they secreted albumin and not alpha-fetoprotein; and the cellular RNA/DNA ratio rose progressively in culture. The isolation procedure and the duration of culture affected expression of specific P450s differently. CYP1A2, CYP2C9, and CYP2E1 mRNAs were not altered by cell isolation, and levels of CYP1A2 and CYP2C9 mRNA were also maintained for 8 days in culture, whereas CYP2E1 mRNA declined to 9% of values in fresh hepatocytes by day 8. CYP3A4 mRNA content was considerably decreased in freshly isolated hepatocytes compared with normal liver, and expression of this gene during the course of culture was more variable than that of the other P450s. Use of Williams' E medium considerably enhanced accumulation of CYP3A4 mRNA, compared with modified Waymouth 752/1 medium, but had a detrimental effect on levels of the other P450 mRNAs. Despite high levels of expression at the mRNA level, the microsomal protein contents of CYP1A2, CYP2C9, CYP2E1, and CYP3A4 declined progressively during the course of culture; this decline was most rapid for CYP3A4. These results confirm the potential of primary cultures of well-differentiated human hepatocytes for studies of P450 gene regulation in humans, but they also demonstrate that culture conditions are variables that must be carefully controlled when examining liver-specific gene expression in vitro. In particular, time in culture may variably affect expression of P450 enzyme changes at both the mRNA and protein levels.

Extended primary culture of human hepatocytes in a collagen gel sandwich system

To develop a strategy for extended primary culture of human hepatocytes, we placed human hepatocytes between two layers of collagen gel, called a "collagen gel sandwich." Maintenance of hepatocellular functions in this system was compared with that of identical hepatocyte preparations cultured on dry-collagen coated dishes or cocultured with rat liver epithelial cells. Human hepatocytes in a collagen gel sandwich (five separate cultures) survived for more than 4 wk, with the longest period of culture being 78 d. They maintained polygonal morphology with bile canaliculuslike structures and high levels of albumin secretion throughout the period of culture. In contrast, hepatocytes on dry-collagen became feature-less, and albumin secretion could not be detected after 14 d of culture. This loss of albumin secretion was partially recovered by overlaying one layer of collagen gel. Ethoxyresorufin O-deethylase activity, associated with cytochrome P450 1A2, was detected basally up to 29 d in collagen gel sandwich culture. These activities were induced four- to eightfold after induction with dibenz(a,h)anthracene. Cocultures also maintained basal activity up to 29 d. However, their inducibility was lower than that of hepatocytes in collagen gel sandwich. No ethoxyresorufin O-deethylase activity was detected in hepatocytes cultured on dry-collagen at 7 d. Thus, the collagen gel sandwich system preserves differentiated morphology and functions of human hepatocytes in primary culture for a prolonged period of time. This system is a promising model for studying human hepatocellular function, including protein synthesis and drug metabolism in vitro.

Differences in the regulation of cytochrome P450 family members during liver regeneration

BACKGROUND/AIMS

Cytochrome P450 enzymes (P450s) metabolise endogenous substances and a vast variety of drugs. Little is known about the regulation of P450s during pathophysiological conditions in the liver. Therefore we studied the regulation of P450 1A1, 1A2, 2E1 and 3A during liver regeneration after two-thirds hepatectomy.

METHODS

Partial hepatectomy or sham surgery was performed in Sprague-Dawley rats. At different time points after surgery, microsomal proteins were isolated and the RNA was prepared. Northern blot analysis, Western blot analysis and enzyme assays for the different P450s were performed.

RESULTS

Northern blot analysis showed a transient downregulation of cytochromes P450 1A2 and 2E1 after hepatectomy, while the expression of cytochrome P450 3A remained unaffected. Western blot analysis of microsomal proteins showed that changes of the mRNA levels are not reflected in the protein level, most likely because the half-life of the P450 proteins in hepatocytes is long, and thus a transient mRNA downregulation has little impact on the total amount of protein detected. Differences in the regulation of the enzymatic activities were found for P450 1A2 and 2E1. Interestingly, the metabolic activity of cytochrome P450 2E1 decreased dramatically post-hepatectomy, while the P450 2A1 activity remained unchanged.

CONCLUSIONS

Regulatory mechanisms were found on the RNA level and by post-translational mechanisms which downregulate P450 expression and activity during liver regeneration. These results indicate prolonged half-life of drugs during hepatocyte proliferation, and thus also have important implications for therapy in humans.

Expression of cytochrome P450 isoforms in rat hepatic stellate cells

The current study evaluated the expression and the inducibility of cytochrome P450 isoforms in rat hepatic stellate cells (HSCs). Immunoblotting study revealed that HSCs expressed several P450s and CYP2C11, 3A2, and 2D1 were major isoforms. The levels of CYP2B1, 2C11, 2D1, 2E1, and 3A2 in HSCs were 14 - 38% of those in hepatocytes. CYP1A2 content was similar in each cell type. These P450 levels in HSCs gradually decreased during culture as seen in hepatocytes; the level of CYP3A2 rapidly, whereas that of CYP2D1 slowly decreased. Phenobarbital, a typical inducer of CYP3A2 and 2B1 increased CYP3A2 level as well, but had less potency in the induction of CYP2B1 in HSCs. These results indicate that multiple P450 isoforms were present in HSCs, but their content and inducibility were different between HSCs and hepatocytes.

Characterization of the human cytochrome P4502D6 promoter. A potential role for antagonistic interactions between members of the nuclear receptor family

The functional mapping of the human cytochrome P4502D6 (CYP2D6) promoter in HepG2 cells revealed the presence of both positive and negative regulatory elements. One of these regulatory elements overlapped a sequence that is highly conserved in most members of the CYP2 family. This element, which consists of a degenerate AGGTCA direct repeat spaced by 1 base pair (DR1) and is known to be a target for members of the steroid receptor superfamily, was found to bind in vitro translated hepatocyte nuclear factor 4 (HNF4) in gel retardation analysis. Using HepG2 nuclear extracts, three protein-DNA complexes were formed on the DR1 element, one of which was confirmed to be dependent on the binding of HNF4. The other DR1 complexes were shown to be due to the interaction of the orphan receptor chicken ovalbumin upstream promoter transcription factor I (COUP-TFI). Experiments in COS-7 cells showed that HNF4 could activate the CYP2D6 promoter 30-fold. Surprisingly, mutation of the DR1 element produced a relatively minor 23% decrease in activity in HepG2 cells. Additionally, COUP-TFI was shown to inhibit HNF4 stimulation of the CYP2D6 promoter in COS-7 cells, suggesting that COUP-TFI could attenuate the effect of HNF4 in HepG2 cells. However, when HNF4 levels were increased in HepG2 cells by co-transfection, it resulted in the enhancement of CYP2D6 promoter activity, indicating that HNF4 could overcome the repressive effect of COUP-TFI. Therefore, the contribution of the DR1 element in controlling the transcription of the CYP2D6 gene depends on the balance between positively and negatively acting transcription factors.