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Biomedical subjects

S H Yap

Publications and source records attributed to S H Yap.

At least 19 recordsLinked to original sources
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↗
PubMed1991

Tumor necrosis factor (TNF) inhibits interleukin (IL)-1 and/or IL-6 stimulated synthesis of C-reactive protein (CRP) and serum amyloid A (SAA) in primary cultures of human hepatocytes.

Interleukin (IL)-1, IL-6 and tumor necrosis factor (TNF) are considered as important mediators for the modulation of liver synthesis of acute phase proteins. However, studies of the direct effect of individual or a combination of these cytokines on the synthesis of acute phase proteins in human hepatocytes are still very limited. In this study, we have examined the synthesis of C-reactive protein (CRP) and serum amyloid A (SAA) in primary cultures of human hepatocytes exposed to recombinant(r)IL-1 alpha (100 U/ml), rIL-6 (2000 U/ml), rTNF alpha (30 U/ml) and to various combinations of these cytokines in the presence of 1 microM dexamethasone. Monoclonal antibodies to rTNF alpha and monospecific anti-rIL-6 sheep antiserum were also used to investigate the possible endogenous production of TNF or IL-6. The findings indicate: (1) IL-1 and IL-6 are stimulatory cytokines for the liver synthesis of CRP and SAA. Anti IL-6 abolishes the stimulatory effect of IL-1. These findings support the previous observation and indicate that IL-1 exerts its action on the enhanced synthesis of CRP and SAA at least in part via IL-6 production in the liver cell. (2) TNF is an inhibitory cytokine for the liver synthesis of CRP. It inhibits also the stimulatory effect of IL-1 and IL-6 on the synthesis of CRP and SAA. (3) Since anti-TNF enhances the stimulatory effect of IL-6 on the synthesis of CRP and SAA, it seems likely that TNF is also produced by the human hepatocytes. However, further studies for more direct evidence of the liver cell production of TNF, such as the detection of TNF messenger RNA are required.

Adult↗
PubMed1991

Surrogate markers are not useful for identification of HCV carriers in chronic hemodialysis patients.

Several diagnostic hepatitis C assays have been developed for the detection of antibodies to different antigens of the virus. This virus is the major cause of non-A, non-B hepatitis. Seventy-nine patients undergoing chronic hemodialysis and/or hemofiltration were tested for the presence of anti-HCV antibodies (anti-C-100-3 antibodies and anti-core antibodies), anti-hepatitis B core antibodies (anti-HBc), and aminotransferases (ALT). Seven patients were positive by one or more of the anti-HCV enzyme linked immunoassays (EIAs), while HCV-RNA was detectable in only four patients. These four patients had at least one, but not necessarily the same, positive anti-HCV EIA. HCV-RNA was not detected in patients who had no antibodies as determined by all six anti-HCV EIAs. All patients with a marker for HCV infection had persistent normal levels of transaminases. Three patients had elevated ALT values without a marker for HCV infection and suffered from hepatitis B virus infection. Anti-HBc was detected in 27/72 patients without any marker and in four patients with a marker of HCV infection. However, HCV-RNA was detectable in only one of these four anti-HBc positive patients. It is concluded that surrogate markers (anti-HBc and serum transaminases) are not useful for identification of HCV carriers in chronic hemodialysis patients.

Biomarkers↗
PubMed1991

Identification of plasma membrane proteins involved in the hepatocyte invasion of Plasmodium falciparum sporozoites.

To determine whether surface proteins of hepatocytes might be involved in the sporozoite invasion, plasma membrane proteins were prepared from human livers with CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulphonate) and radiolabelled with 125I (Iodogen; 1,3,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril). The labelled proteins were incubated with Plasmodium falciparum sporozoites and cross-linked with DSP (dithio-bis-succinimidylpropionate). Radiolabelled proteins released by reduction after repeated washing of the sporozoite-complex were separated by SDS-PAGE and autoradiographed. Two human hepatocyte membrane proteins of 20 and 55 kDa were found to be involved in the initial binding of P. falciparum sporozoites. The electrophoretically purified 20- and 55-kDa proteins both inhibited the binding of the corresponding radiolabelled proteins to P. falciparum sporozoites and reduced the invasion of sporozoites in an in vitro assay. We propose that these 20-kDa and 55-kDa proteins represent putative human hepatocyte receptors for P. falciparum sporozoite invasion.

Animals↗
PubMed1991

Nodular regenerative hyperplasia of the liver: an important cause of portal hypertension in non-cirrhotic patients.

In our hospital over the last 10 years a diagnosis of nodular regenerative hyperplasia was made for 13 patients. Sixty-nine percent of these patients had portal hypertension, representing 27% of all our patients with portal hypertension and a non-cirrhotic liver. Nodular regenerative hyperplasia was the second most frequent cause of portal hypertension in patients without cirrhosis. To make the diagnosis, a reticulin staining of a surgical biopsy is most helpful. However, the characteristic derangement of the liver architecture on histology may still be overlooked. In this study a suggestive relation was found between malignant disease (multiple myeloma, chronic myelogenous leukaemia, Leydig cell tumour and Hodgkin's disease), the use of cytotoxic or immunosuppressive drugs and nodular regenerative hyperplasia. Furthermore, a high rate of symptomatic nodular regenerative hyperplasia was observed in patients following kidney transplantation. Liver function abnormalities developed in these patients after a period ranging from 8 months to 3 years of immunosuppressive- or chemotherapy. These liver function abnormalities were, however, usually mild. Since hepatic encephalopathy is not likely to develop in these patients with nodular regenerative hyperplasia a decompressive shunt operation is a good alternative approach, if not the treatment of choice, for the prevention of recurrent variceal haemorrhage.

Adolescent↗
PubMed1991

Intrahepatic cholestasis induced by amoxicillin/clavulanic acid (Augmentin): a report on two cases.

Two patients who developed a severe but reversible cholestatic jaundice during and after treatment with an amoxicillin/clavulanic acid preparation (Augmentin) are described. The diagnosis of drug-induced intrahepatic cholestasis was based on the clinical course, biochemical pattern and on histological findings. Since amoxicillin alone does not induce liver injury, the combination of amoxicillin and clavulanic acid or clavulanic acid alone could be responsible for this adverse reaction, probably through a metabolic idiosyncrasy or a hypersensitivity mechanism. Although more than 100 cases of hepatotoxic reactions have been reported to the pharmaceutical company (Beecham Laboratories) and several reports have been published, the incidence of hepatotoxicity of this antibiotic is relatively rare, since this antibiotic has been widely used. However, recognition of this benign and reversible cholestatic syndrome is important to avoid unnecessary, expensive and invasive diagnostic procedures.

Aged↗
PubMed1991

The role of methanethiol in the pathogenesis of hepatic encephalopathy.

Mixed disulfides of methanethiol represent a relative estimate for an exposure to methanethiol. The concentrations of methanethiol-mixed disulfides, methionine, 4-methylthio-2-oxobutyrate and ammonia were measured in patients with different stages of hepatic encephalopathy, in patients with chronic kidney failure and in healthy subjects. In patients with hepatic encephalopathy, the mean serum concentrations of all these compounds were elevated. However, the elevations of methanethiol-mixed disulfides were small and partly caused by decreased renal function. In addition, the levels of methanethiol-mixed disulfides did not differ significantly between the different grades of hepatic encephalopathy. The concentrations of methanethiol-mixed disulfides were substantially lower than those previously observed in healthy subjects after an oral methionine load or in a patient with a deficiency in methionine adenosyltransferase, the latter without causing encephalopathy. We concluded that the role of methanethiol in the pathogenesis of hepatic encephalopathy is probably minor, if not insignificant. In the patients with hepatic encephalopathy, a significant correlation was found between the concentrations of methionine and 4-methylthio-2-oxobutyrate and between 4-methylthio-2-oxobutyrate and methanethiol-mixed disulfides, supporting the theory that methanethiol is formed by way of the methionine transamination pathway. Evidence is provided that, besides the methionine transsulfuration pathway, the transamination pathway is also impaired in patients with hepatic encephalopathy.

Adult↗
PubMed1990

The effect of beclobric acid and clofibric acid on peroxisomal beta-oxidation and peroxisome proliferation in primary cultures of rat, monkey and human hepatocytes.

The peroxisome-proliferating effects of clofibric acid and beclobric acid were studied in primary cultures of hepatocytes derived from rat, monkey (Macaca fascicularis) and human liver. Determination of peroxisomal fatty acid beta-oxidation and morphometrical analysis of the peroxisomal compartment were performed after incubation of 1-day-old hepatocyte cultures for 3 days with either compound. In rat liver cell cultures both compounds gave a 10-fold increase in peroxisomal beta-oxidation, a 3-fold increase in the relative number of peroxisomes and a 1.5-fold increase in the mean size of peroxisomes. Beclobric acid gave its maximal effect at a concentration of 10 microM, which is at least one order of magnitude lower than the maximum-effect concentration of clofibric acid. At concentrations greater than 300 microM beclobric acid was cytotoxic. No stimulation of peroxisomal fatty acid beta-oxidation was found in either monkey or human hepatocyte cultures. Morphometrical analysis also showed no increase in the peroxisomal compartment in cultures derived from these species, as indicated by the lack of increase in both relative number and size of peroxisomes. In all three species tested beclobric acid was equally cytotoxic for hepatocytes in vitro. These results are of relevance for the interpretation of the peroxisome-proliferating effects of clofibrate and similar compounds in rats. Since peroxisome proliferation may be correlated to increased hepatic tumour incidences in the rat, the absence of peroxisome proliferation in primates suggests the absence of tumourogenic activity by hypolipidemic compounds in these species.

Adult↗
PubMed1990

Binding of the major and large HBsAg to human hepatocytes and liver plasma membranes: putative external and internal receptors for infection and secretion of hepatitis B virus.

A likely mechanism of the strong hepatotrophism of the hepatitis B virus is the presence of specific receptors for the surface antigen of hepatitis B virus on hepatocyte membranes. To examine this hypothesis, we have performed binding studies using recombinant large (preS1 + preS2 + S) and major (S) proteins with adult human hepatocytes, rat hepatocytes, human fibroblasts, human peripheral blood mononuclear cells and plasma membranes derived from these cell types. We found that major HBsAg was able to bind specifically to human hepatocytes, human fibroblasts and human blood mononuclear cells. This binding could be inhibited by recombinant middle (preS2 + S) protein but not by the recombinant large protein. No binding could be demonstrated between large HBsAg and human hepatocytes. However, large protein bound specifically to plasma membranes derived from human liver tissue, human fibroblasts and HepG2A16 cells. This binding could be partially inhibited by the major protein and by a synthetic preS1 peptide but not by a synthetic preS2 peptide. These results support the assumption that hepatitis B virus absorption and penetration into human hepatocytes is mediated by specific receptors recognizing an amino acid sequence in the S-region. This recognition site is not displayed by the recombinant large protein. However, the large protein is recognized by its preS1 region and by a second binding site in the S-region by a receptor molecule, located on the inner surface of the plasma membranes or intracellular membranes of human hepatocytes and of some other cell types derived from human tissue.

Animals↗
PubMed1990

Hepatitis B pre-S1 and pre-S2 proteins: clinical significance and relation to hepatitis B virus DNA.

Pre-S proteins may have an important role in virus assembly and virus entry into the host cell. The presence of pre-S proteins in serum has also been thought to correlate with active viral replication. To investigate whether pre-S proteins in serum might have additional diagnostic and/or predictive value for liver sequelae in HBV infection, sera from six different serological groups of patients with HBV markers (total number 363) and different manifestations of liver histology were examined for the presence of pre-S1 and pre-S2 proteins using micro-ELISAs. Pre-S1 and pre-S2 proteins were detected significantly more often in HBV-DNA-positive than in HBV-DNA-negative sera from HBsAg carriers. However, pre-S1 and pre-S2 proteins were also found in HBV-DNA-negative HBsAg carriers irrespective of serum HBeAg/anti-HBe or liver histologic findings. These results suggest that the presence of the pre-S1 and or pre-S2 proteins in serum either does not seem to reflect the presence of active viral replication and active liver disease or pre-S proteins are more readily detectable than HBeAg and HB-DNA as measured by a dot-blot technique. Furthermore, the presence of pre-S proteins in serum is strongly correlated with that of HBsAg.

Chronic Disease↗
PubMed1990

Differential effects of endotoxin and fibrinogen degradation products (FDPS) on liver synthesis of fibrinogen and albumin: evidence for the involvement of a novel monokine in the stimulation of fibrinogen synthesis induced by FDPS.

1. Administration of endotoxin or fibrinogen degradation products (FDPs) in rats increase fibrinogen synthesis comparable to that found during the acute phase response. 2. An increased fibrinogen synthesis is also found in co-cultures of hepatocytes with peripheral blood mononuclear cells upon administration of endotoxin or FDPs, but not in primary cultures of hepatocytes alone. 3. However, the increased synthesis of fibrinogen by FDPs is not accompanied by a decreased albumin synthesis, as in the case of stimulated fibrinogen synthesis induced by endotoxin in vivo and in co-cultures of hepatocytes with peripheral blood mononuclear cells, or induced by monocytic products in vivo and in primary cultures of hepatocytes alone. 4. Since IL-1 and/or IL-6 could not be accounted for the stimulation of fibrinogen synthesis without a decreased albumin synthesis, a novel monokine produced by mononuclear cells upon FDP administration might be involved.

Albumins↗