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Biomedical subjects

J L Ding

Publications and source records attributed to J L Ding.

50 records · Page 3Linked to original sources
PubMed1989

Differential susceptibility of a fish, tilapia Oreochromis mossambicus (Teleostei, Cichlidae) to hepatocarcinogenesis by diethylnitrosamine and methylazoxymethanol acetate.

Oreochromis mossambicus, commonly known as tilapia, is a freshwater teleost with a wide tolerance to environmental conditions. Multiple focal lesions in the liver were observed 2 months after cessation of a one-month long treatment with 100 p.p.m. diethylnitrosamine. Cells were small and compact and arranged in sheets. Ultrastructurally, these cells have abundant endoplasmic reticulum, round mitochondria, less conspicuous golgi apparatus and fat droplets. Other organs like the intestines, spleen, kidneys, ovaries and pituitary appeared normal. Two liver inducible enzymes, gamma-glutamyl transferase and tyrosine aminotransferase were elevated by 5- and 3-fold respectively. Aggressive migration of hepatocytes was observed in tumorigenic liver explants. Vitellogenesis and early embryological development appeared unaffected as the female fish spawned during hepatocarcinogenesis. However, their fry were stunted and short-lived. To compare the susceptibility of tilapia to another hepatocarcinogen, the fish were also treated with methylazoxymethanol acetate at 10 p.p.m. for 0.5-1 h. However, methylazoxymethanol acetate was too toxic and 75% of the fish succumbed 1 day after treatment. Moreover, after 2 months post-treatment, neither tumors nor change in enzyme activities were observed in any organ. These results suggest that tilapia could be a useful model for screening and differentiating carcinogens since they could develop liver tumors within only 2 months after treatment with diethylnitrosamine.

Animals↗
PubMed1989

Stellate- and foci-formation of mouse fibroblast cells transfected with various cancer cell DNA.

Two methods of DNA-mediated gene-transfer, namely, CaPO4 co-precipitation and polybrene/DMSO-induction were used to analyse oncogenes from various cancer cell-lines. Third time transfection of mouse fibroblast cells, NIH/3T3 with 10, 100, 1,000 and 3,000 ng of DNA from spontaneous human hepatoma cells produced 41, 4, 45 and 56 foci, respectively. It appears that 100 ng of this hepatoma cell DNA gave the least effective transformation ability. However, with two spontaneous mammary cancer cell lines, 100 ng DNA gave the highest number of foci. In general, during the initial transfection, the cells appeared semi-transformed, showing stellate growth patterns. With repeated transfections they gave way to foci. However, with aflatoxin-induced rat hepatoma cell (JB-1) DNA, only stellate growths persisted to indicate intermediate transformation. Transfection of the epithelial-like normal rat liver cell line, BL8 with JB-1 DNA produced haphazard growth pattern, although a hepatoma-associated enzyme, gamma-glutamyl transferase was introduced into the BL8 cells which previously had no detectable enzyme activity.

Animals↗
PubMed1988

Pokeweed mitogen stimulates DNA synthesis in cultured amoebocytes of Carcinoscorpius rotundicauda.

Cultures of Carcinoscorpius rotundicauda amoebocytes in Grace's insect (modified) medium supplemented with 20% foetal bovine serum, were stimulated with pokeweed mitogen at 0.5 to 50 micrograms/ml for 24 to 72 h at 26 degrees C. DNA synthesis was monitored by measuring the uptake of 3H-thymidine. The optimal concentration of pokeweed mitogen was established at 2.5 micrograms/ml. The ideal duration of stimulation was 48 h. Under these conditions, amoebocyte cultures showed increases in uptake of 3H-thymidine up to 55-fold. Attempts at stimulation of these amoebocytes with phytohaemagglutinin, concanavalin A and endotoxin showed no increase in 3H-thymidine uptake. Nevertheless, positive stimulation by pokeweed mitogen demonstrates the potential of such an approach to establishing a permanent amoebocyte cell line for lysate production. This stimulation was reversed by 5 mM hydroxyurea, suggesting a true induction of DNA synthesis.

Amoeba↗
PubMed1987

Enhancement of specific [3H]ouabain binding and ouabain sensitive 86rubidium influx in intact human lymphocytes by a dialysable factor in human and fetal calf serum.

We have measured specific [3H]ouabain binding and ouabain sensitive 86rubidium influx in intact human lymphocytes incubated for up to 7 days in media containing different concentrations of fetal calf serum and human serum. Incubation for periods of up to 7 days with fetal calf serum and human serum produced increases in both specific [3H]ouabain binding and ouabain sensitive 86rubidium influx that were dependent on concentration and time. Neither specific [3H]ouabain binding nor ouabain sensitive 86rubidium influx was altered when dialysed serum was used, suggesting that both fetal calf serum and human serum contain a dialysable factor or factors which stimulate specific [3H]ouabain binding and ouabain sensitive 86rubidium influx in intact human lymphocytes. To further elucidate the mechanisms underlying these changes we also measured the activity of two other enzymes of the lymphocyte plasma membrane, 5'-nucleotidase and gamma-glutamyltransferase, the uptake of [3H]thymidine by the intact cells, and the effects of cycloheximide, puromycin, and anisomycin, inhibitors of protein synthesis. The activity of 5'-nucleotidase was increased after incubation of the lymphocytes in fetal calf serum for 72 h, but the activity of gamma-glutamyltransferase was not changed, suggesting some selectivity of the stimulatory effect. Measurements of [3H]thymidine uptake by the lymphocytes showed that the major part of the observed changes in specific [3H]ouabain binding and ouabain sensitive 86rubidium influx was not attributable to transformation of the lymphocytes to lymphoblasts. All three inhibitors of protein synthesis prevented the increase in specific [3H]ouabain binding due to fetal calf serum.

5'-Nucleotidase↗
PubMed1985

Hepatitis B infection in households of acute cases.

Seroepidemiological studies conducted in 369 household contacts of 80 acute cases of hepatitis B in Singapore showed that asymptomatic chronic carriers of hepatitis B surface antigen (HBs Ag) are the main source of acute hepatitis B infection. The HBs Ag prevalence rate in asymptomatic household members was 20% compared with a 6% prevalence for the general population. The majority of the household carriers (60%) were highly infectious with positive hepatitis e antigen (HBe Ag). The overall prevalence of HBV infection (with at least one HBV marker) of the household contacts was 40.7%. Spouses and parents of acute cases had a significantly higher prevalence of HBV infection than other members of the families. HBV prevalence rate showed no association with the household size. Factors associated with the risk of transmission of HBV infection included sharing of various personal and household articles, such as toothbrush, towel, handkerchief, clothing, razor, comb, bed and bedding. Sleeping in the same bedroom, eating together at meals, and sharing of eating and drinking utensils were not associated with an increased risk of transmission of infection. Follow-up studies six months later showed that 30% of the acute cases became chronic HBs Ag carriers (with 46% HBe Ag positive), thus providing an additional source of infection in the families, while 8% of the susceptible household members acquired asymptomatic HBV infection. Health education on the prevention of HBV transmission in the homes of acute cases should be based on sound epidemiological information. Household contacts of acute cases of hepatitis B should be routinely screened and the susceptible vaccinated against the disease as soon as possible.

Acute Disease↗
PubMed1984

Detection of HBeAg in the lymphocytes of sero-HBeAg negative patients with chronic hepatitis B and primary hepatocellular carcinoma.

HBeAg has been detected in the peripheral lymphocytes of chronic hepatitis B patients who were seronegative for HBeAg. Nearly 50% of these patients (males, aged 41-66) had histology confirmed hepatocellular carcinoma while the normal carriers (males, aged 22-37) showed histological changes of chronic persistent or chronic active hepatitis. The HBeAg was also demonstrated in the lymphocytes of eight voluntary blood donors who were found to be seropositive for HBsAg and HBeAg. The lymphocyte HBeAg exists in two subentities; a soluble and a particulate form. These observations suggest that the peripheral blood lymphocytes are hosts for HBV replication and production of infectious virus particles. Such processes may lead to an impaired immune defence mechanism, and explain the chronicity of the disease, and hepatic oncogenesis.

Adult↗
PubMed1984

An epidemic of cockles-associated hepatitis A in Singapore.

An epidemic of serologically confirmed hepatitis A occurred between May and September 1983 in Singapore. The vehicle of transmission was traced to raw and partially cooked cockles, Anadara granosa, which had been imported from places with no sanitary control on the production. Strict controls on imported cockles are warranted.

Adolescent↗
PubMed1982

In situ determination of the molecular weight of hepatic gamma-glutamyl transferase and gamma-glutamyl hydrolase activities.

The molecular weight of gamma-glutamyl transferase from normal rat liver and hepatoma tissue was determined by radiation-inactivation and found to be approx 100000 in each case. The molecular weight previously reported for the subunit containing the gamma-glutamyl binding site (22000) is considerably less than that of the holoenzyme, suggesting that in situ the large subunit is implicated in both transferase and hydrolase activities.

Animals↗
PubMed1981

Subcellular localization and isolation of gamma-glutamyltransferase from rat hepatoma cells.

Cultured rat hepatoma cells were homogenized and subjected to subcellular fractionation by analytical sucrose density centrifugation to determine the localization of gamma-glutamyltransferase ((5-glutamyl-)-peptide: amino acid 5-glutamyltransferase, EC 2.3.2.2). The activity was exclusively localized to the plasma membrane. Diazotized sulphanilic acid was used as a non-penetrant membrane reagent which inactivates ectoenzymes. With both intact and sonicated cells, only 70-75% inhibition of gamma-glutamyltransferase activity was observed. At least 12% of the total cell complement of gamma-glutamyltransferase activity is highly resistant to inactivation by diazotized sulphanilic acid even after Triton X-100 solubilization. The enzyme was purified from hepatoma cells and its properties compared with enzyme from normal liver. Apart from the striking increase in Vapp there were only minor differences between the enzymes from the two sources. In contrast to the complete abolition of transpeptidase activity of the purified hepatoma enzyme by diazotized sulphanilic acid, the hydrolytic activity of this preparation was only slightly inhibited.

Animals↗
PubMed1981

Purification and properties of gamma-glutamyl transferase from normal rat liver.

gamma-Glutamyl transferase ((5-glutamyl)-peptide: amino-acid 5-glutamyltransferase, ED 2.3.2.2) has been partially purified from both whole rat liver (600-fold) and from isolated biliary tract (1200-fold). The most highly purified fraction gave two protein bands on polyacrylamide gel electrophoresis, the major band alone having enzyme activity. The enzyme purified from biliary tract appears identical to that from whole liver preparation according to molecular weight, kinetic parameters and the effects of various inhibitors. Three liver cell-types; parenchymal, Kupffer and biliary tract were isolated by perfusion of the rat liver in situ with collagenase, followed by selective cell isolation. Approx. 80-90% of the total recovered enzyme activity was found in the biliary tract. Nearly 50% of the apparent enzyme activity in the parenchymal cell was attributable to a nonspecific hydrolase.

Animals↗