Search PubMed⌕ Search

Biomedical subjects

S H Yap

Publications and source records attributed to S H Yap.

At least 55 records · Page 3Linked to original sources
PubMed1994

Rapid clearance of hepatitis C virus RNA in peripheral blood mononuclear cells of patients with clotting disorders and chronic hepatitis C treated with alpha-2b interferon is not a predictor for sustained response to treatment.

Thirteen patients with congenital coagulation disorders and chronic hepatitis C were treated with alpha-interferon (IFN). Serum transaminases (ALT) and hepatitis C virus (HCV)-RNA in plasma and peripheral blood mononuclear cells (PBMC) were followed during and after treatment. During IFN treatment ALT levels normalized in 8/13 patients. In all patients HCV-RNA disappeared from PBMC. In 9/13 HCV-RNA also became undetectable from plasma; in six of these nine this occurred earlier in PBMC than in plasma; in the remaining three the disappearance of HCV-RNA occurred simultaneously in plasma and PBMC. All but two patients relapsed within 3 weeks after cessation of IFN, one relapsed after 6 weeks and one patient remains in remission after 6 months. HCV-RNA reappeared either earlier in plasma (3/12) or simultaneously in plasma and PBMC (9/12). Viral replication in PBMC thus can easily be suppressed by IFN, whereas longer treatment is needed for the eradication of HCV-RNA in plasma. The detection of HCV-RNA in PBMC cannot be used as a prognostic marker for the identification of patients with chronic hepatitis C who will have a sustained response to IFN treatment.

Adult↗
PubMed1994

Hepatitis delta virus attaches to human hepatocytes via human liver endonexin II, a specific HBsAg binding protein.

Recently we identified human liver endonexin II (EII) as a specific hepatitis B surface antigen (HBsAg) binding protein. To investigate whether EII is also able to interact with the HBsAg envelope of the hepatitis delta virus (H delta V), immunoprecipitation experiments were performed. H delta V particles could be co-precipitated by polyclonal rabbit anti-EII, but not by rabbit anti-glutathiontransferase (GST pi) antibodies from an H delta V-enriched fraction containing EII or GST pi. These findings suggest that H delta V particles were co-precipitated by anti-EII as a consequence of the binding between HBsAg present in the H delta V envelope and EII. Furthermore, binding of H delta V particles to human hepatocytes could be inhibited by incubation of the liver cells with rabbit anti-EII IgG or the H delta V particles with anti-idiotypic (anti-HBsAg) antibodies, developed spontaneously in rabbits immunized with EII. These findings support the assumption that small HBsAg present in the H delta V envelope is important for the attachment to the hepatocytes and that EII plays an important role in this process.

Adhesiveness↗
PubMed1994

Spontaneous development of anti-hepatitis B virus envelope (anti-idiotypic) antibodies in animals immunized with human liver endonexin II or with the F(ab')2 fragment of anti-human liver endonexin II immunoglobulin G: evidence for a receptor-ligand-like relationship between small hepatitis B surface antigen and endonexin II.

In a previous study, we have identified endonexin II (E-II) on human liver plasma membranes as a specific, Ca(2+)-dependent, small hepatitis B surface antigen (HBsAg)-binding protein. In this article, we describe the spontaneous development of anti-HBs antibodies in rabbits immunized with native or recombinant human liver E-II and in chickens immunized with the F(ab')2 fragment of rabbit anti-human liver E-II immunoglobulin G. Anti-HBs activity was not observed in rabbits immunized with rat liver E-II. Cross-reactivity of anti-E-II antibodies to HBsAg epitopes was excluded, since anti-HBs and anti-E-II activities can be separated by E-II affinity chromatography. The existence of an anti-idiotypic antibody is further demonstrated by competitive binding of human liver E-II and this antibody (Ab2) to small HBsAg, suggesting that Ab2 mimics a specific E-II epitope that interacts with small HBsAg. In addition, it was demonstrated that anti-HBs antibodies developed in rabbits after immunization with intact human liver E-II or in chickens after immunization with F(ab')2 fragments of rabbit anti-human liver E-II immunoglobulin G recognize the same epitopes on small HBsAg. These findings strongly indicate that human liver E-II is a very specific small HBsAg-binding protein and support the assumption that human liver E-II is the hepatitis B virus receptor protein.

Animals↗
PubMed1994

Interindividual variation in biotransformation and cytotoxicity of bromobenzene as determined in primary hepatocyte cultures derived from monkey and human liver.

1. Bromobenzene-evoked hepatotoxicity resulting from cytochrome P450-mediated epoxidation has been studied extensively in rodents in vivo and in rodent hepatocytes. In this paper we present data concerning the formation of bromphenols, glutathione (GSH) depletion and cytotoxicity observed in primate hepatocytes in primary culture after exposure to bromobenzene (BrB). 2. After pre-incubation for 2 or 24 h, hepatocytes were exposed to BrB in concentrations up to 2 mM for 4 or 24 h. 3. In both human and cynomolgus monkey hepatocytes BrB cytotoxicity and GSH depletion were found after exposure to 2 mM BrB. The degree of the observed effects was not influenced by the duration of pre-incubation and/or exposure periods. 4. Major inter-individual differences were observed, which could not be attributed to differences in cytochrome P450-mediated bioactivation rates. This suggests that the variation in individual susceptibility to BrB may be related to inter-individual differences in the activity of de-activating (metabolic) pathways. 5. The study of the background of these inter-individual differences may contribute to a more complete understanding of the factors ruling sensitivity to BrB or related chemicals.

Animals↗
PubMed1993

Regulation of glycogen phosphorylase activity in isolated human hepatocytes.

Hepatocytes were isolated from human liver tissue by a two-step perfusion technique. They were treated with vasopressin, angiotensin, ATP and phenylephrine, which are known to be Ca(2+)-mediated glycogenolytic agents in rat liver tissue, and as a control, they were treated with the cyclic AMP-mediated hormones glucagon and isoproterenol. All agonists induce a time-dependent activation of glycogen phosphorylase. Glucagon and isoproterenol induce a somewhat higher degree of phosphorylase activation compared with vasopressin, angiotensin, ATP and phenylephrine, which all increase inositol tris-phosphate levels and have no effect on the cyclic AMP levels. The total activity of glycogen phosphorylase (a + b), amounting to 30 to 35 mU/mg protein, is found to be much lower than that found in rat liver tissue. Because only minor differences could be found, we conclude that the regulation of glycogen phosphorylase in human liver tissue is basically the same as that found in rat liver tissue.

Adenosine Triphosphate↗
PubMed1993

Endonexin II, present on human liver plasma membranes, is a specific binding protein of small hepatitis B virus (HBV) envelope protein.

Binding of viral envelope proteins to specific receptors on human hepatocytes is considered to be an important step in HBV infection. In this study, we demonstrate that a 34-kDa human liver plasma membrane protein specifically binds to small HBsAg in a Ca(2+)-dependent manner. By partial amino acid sequence analysis of preparatively isolated 34-kDa protein comigrating with HBsAg-binding protein obtained from binding assay on IEF/SDS-PAGE, we have identified this HBsAg-binding protein as Endonexin II (E-II). Native human liver E-II inhibits binding of HBsAg to intact human hepatocytes and shows specific binding to small HBsAg. This binding can be inhibited by human liver plasma membrane proteins, recombinant E-II, or anti-E-II antibodies. Despite 90% sequence homology, rat liver E-II does not bind to small HBsAg and does not inhibit significantly (less than 20%) binding of HBsAg to intact hepatocytes. Cross-linking of small HBsAg and radiolabeled human liver E-II resulted in a specific additional protein complex on PAGE with an apparent molecular weight of 90 kDa, corresponding to a complex of E-II and small HBsAg with a ratio of 2 to 1 or 1 to 2. These findings indicate that E-II, found in human liver, is a specific HBsAg-binding protein and might play an important role in the initiation of HBV infection.

Amino Acid Sequence↗
PubMed1993

Plasma collected from heparinized blood is not suitable for HCV-RNA detection by conventional RT-PCR assay.

Detection of hepatitis C virus-RNA (HCV-RNA) in serum or in plasma is considered a reliable marker for ongoing HCV infection. HCV-RNA was measured routinely in plasma collected from heparinized blood of patients with chronic hepatitis C and varying results were found. In this study, HCV-RNA was detected in peripheral blood mononuclear cells (PBMCs) and in serum of 16 out of 17 anti-HCV positive patients with chronic hepatitis C. In contrast, HCV-RNA was found in plasma collected from heparinized blood of only one of these seventeen patients. The addition of heparin to known HCV-RNA containing solutions before reverse-transcription and separately before PCR, demonstrated the inhibitory effect of heparin on the reverse transcription and amplification reaction. Furthermore, evidence is provided that plasma for PCR should be collected preferably into EDTA vacutainers. It is concluded, therefore, that plasma collected from heparinized blood is not suitable for HCV-RNA determination by RT-PCR. In addition, PBMCs might play an important role in the pathobiology of hepatitis C virus, since HCV-RNA was easily detected in PBMC of patients with chronic hepatitis C.

False Negative Reactions↗
PubMed1993

Parathyroid hormone-related peptide expression in primary and metastatic liver tumours.

Parathyroid hormone-related peptide (PTHrP) is a major factor in the pathophysiology of hypercalcaemia of malignancy. Recent evidence suggests that PTHrP may play an important role in the growth and differentiation of neoplastic as well as non-neoplastic cells. PTHrP was originally detected in normal fetal, but not adult, liver. We have used immunocytochemistry to show that reactive human bile ductules expressing a neuroendocrine phenotype contain immunoreactive PTHrP. These observations raised the possibility that PTHrP immunoreactivity may be useful in the differential diagnosis of primary liver tumours and metastases of adenocarcinoma. A total of 24 primary liver tumours and 22 metastases of adenocarcinoma were studied. All cholangiocarcinomas showed immunopositivity for PTHrP and chromogranin A, while all hepatocellular carcinomas were negative for PTHrP and showed only focal and weak positivity for chromogranin A. Mixed types of primary liver tumour contained PTHrP immunoreactivity only in the areas of cholangiocellular differentiation. Moreover, all metastatic adenocarcinomas were negative for PTHrP and chromogranin A except for two out of five metastatic breast adenocarcinomas. These two patients had bone metastases and hypercalcaemia and thus did not yield differential diagnostic problems with cholangiocarcinoma. None of the patients with cholangiocarcinoma and hepatocellular carcinoma had hypercalcaemia. We conclude that PTHrP is a useful marker for primary cholangiocarcinoma, especially in the differential diagnosis of hepatocellular carcinoma and metastatic adenocarcinoma.

Adenocarcinoma↗
PubMed1992

Induction of intercellular adhesion molecule-1 (CD54) on human hepatoma cell line HepG2: influence of cytokines and hepatitis B virus-DNA transfection.

Human hepatocyte expression of intercellular adhesion molecule-1 (ICAM-1) (CD54) was studied in vitro by exposing the well differentiated human hepatoblastoma cell line HepG2 to various cytokines. In addition, hepatitis B virus (HBV)-DNA transfected HepG2 cells were also analysed. Expression of ICAM-1 on HepG2 cells was then revealed with an immunohistochemical procedure. Untreated HepG2 cells were unreactive, but showed strong cytoplasmic ICAM-1 immunoreactivity after treatment with interferon-gamma (IFN-gamma). This induction was completely inhibited by addition of a neutralizing antibody directed to IFN-gamma. IL-1, IL-6, tumour necrosis factor-alpha (TNF-alpha) and IFN-alpha, used alone or in combination, did not induce ICAM-1 expression, neither did they inhibit the IFN-gamma-induced expression of this adhesion molecule on HepG2 cells. Untreated hepatitis B virus-DNA transfected HepG2 cells expressed membranous ICAM-1. These results indicate that IFN-gamma is the main cytokine trigger for ICAM-1 expression on HepG2 cells, suggesting that in areas of liver inflammation this adhesion molecule is up-regulated on hepatocytes by locally released IFN-gamma. In addition, expression of ICAM-1 by hepatitis B virus-DNA transfected HepG2 cells suggests other, still unknown, triggering mechanisms in the induction of such adhesion molecules, for instance gene activation by viral genome, or autocrine virus-induced hepatocellular cytokine production.

Carcinoma, Hepatocellular↗
PubMed1992

Hepatitis C.

Until recently the diagnosis of non-A, non-B hepatitis was made by excluding other detectable viral infections of the liver. Progress in molecular biology made it possible to develop assays which can trace antibodies against the hepatitis C virus. This virus plays a major role in the pathogenesis of transfusion-related and sporadic non-A, non-B hepatitis and possibly of other liver diseases. Although the genome of a few isolates of the hepatitis C virus has already been decoded, the viral particles have not yet been visualized.

Genome, Viral↗
PubMed1991

Inflammation-induced changes in expression and glycosylation of genetic variants of alpha 1-acid glycoprotein. Studies with human sera, primary cultures of human hepatocytes and transgenic mice.

The relative occurrence of genetic variants of human alpha 1-acid glycoprotein (AGP) in relation to changes in glycosylation was studied in sera of patients with burn injury, media of cytokine-treated primary cultures of human hepatocytes and Hep 3B cells, and sera of transgenic mice expressing the human AGP-A gene. It is concluded (i) that the glycosylation of AGP was not dependent on its genetic expression and (ii) that both the variants determined by the AGP-A gene as well as by the AGP-B/B' genes are increased after inflammation or treatment with interleukins 1 and 6.

Animals↗