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T Cheung

Publications and source records attributed to T Cheung.

11 recordsLinked to original sources
PubMed1993

Hypofibrinolysis in patients with hypercoagulability: the roles of urokinase and of plasminogen activator inhibitor.

The prevalence of abnormalities of fibrinolysis in patients with venous thromboembolism is as yet unknown. Defined abnormalities include congenital dysfunction and deficiency of plasminogen, and probably impaired plasminogen activation secondary to elevated levels of plasminogen activator inhibitor type 1 (PAI-1) or to impaired release of tissue plasminogen activator (tPA). In this preliminary study, we analyzed plasma samples from 21 patients for whom an investigation for possible thrombophilia was requested. Twenty of the patients had venous thromboembolism, and one had arterial thrombosis at an early age. Two patients had deficiency of protein C or protein S, but no other recognized biochemical disturbances related to thrombophilia were identified. Patient samples and plasma from 25 normal controls were assayed for tPA activity, PAI-1 activity, and urokinase (uPA) activity and antigen. tPA activity and antigen were not significantly different in patients than in controls. PAI-1 activity was significantly greater in patients (P < 0.0001). uPA activity was not different in the two groups. However, uPA antigen was significantly reduced in patients compared to controls (P = 0.001). These data suggest that hypofibrinolysis leading to a risk of thrombosis may be caused not only by elevated PAI-1 activity but also by reduced total uPA concentration.

Adult↗
PubMed1992

Alzheimer's disease and control brain contain soluble derivatives of the amyloid protein precursor that end within the beta amyloid protein region.

The 39-43 amino acid beta amyloid protein (A beta) that deposits as amyloid in the brains of patients with Alzheimer's disease (AD) is encoded as an internal sequence within a larger membrane-associated protein known as the amyloid protein precursor (APP). In cultured cells, the APP is normally cleaved within the A beta to generate a large secreted derivative and a small membrane-associated fragment. Neither of these derivatives can produce amyloid because neither contains the entire A beta. Our study was designed to determine whether the soluble APP derivatives in human brain end within the A beta as described in cell culture or whether AD brain produces potentially amyloidogenic soluble derivatives that contain the entire A beta. We find that both AD and control brain contain nonamyloidogenic soluble derivatives that end at position 15 of the A beta. We have been unable to detect any soluble derivatives that contain the entire A beta in either the AD or control brain.

Alzheimer Disease↗
PubMed1988

Effect of nutritional zinc-deficiency on O6-alkylguanine-DNA-methyl-transferase activities in rat tissues.

The effect of nutritional zinc-deficiency on the activities of O6-alkylguanine:DNA methyltransferase (AGT) in 9 rat tissues including liver, lung, kidney, spleen, brain, esophagus, forestomach, gastric-stomach and small intestine has been examined. Individual tissue extracts prepared from zinc-deficient and pair-fed, zinc-sufficient rats were incubated with N-[3H]methylnitrosourea-methylated calf thymus DNA for 1 h. The activities of AGT in these tissues were measured by two methods: (a) the transfer of the methyl group from O6-methylguanine in substrate DNA to AGT protein, and (b) the determination of the ratio of O6-methylguanine:7-methylguanine remaining in substrate DNA following incubation. AGT activities (expressed as fmol protein methylated/h per mg protein) were significantly reduced in the esophagus, spleen and lungs of zinc-deficient rats as compared to those in their corresponding zinc-sufficient counterparts. The ratio of O6-methylguanine:7-methylguanine was also reduced in the esophagus of the zinc-deficient rat. These results were consistent with our earlier findings that dietary zinc-deficiency enhances nitrosamine-induced esophageal carcinogenesis in rats.

Animals↗
PubMed1987

Non-cytocidal natural variants of human immunodeficiency virus isolated from AIDS patients with neurological disorders.

To understand the mechanism of HIV-mediated neuropathology five viral isolates were obtained from four AIDS cases with central nervous system manifestations as the primary involvement. The isolates were identified as HIVs by antigenic cross-reactivity and nucleic acid hybridizations to HIV-specific antibodies and DNA probes. The replication and cytopathic properties of these isolates were studied and compared with lymphadenopathy-associated virus (HIVLAV). All isolates had replication competence equivalent to LAV, but four isolates did not kill T4 (CD-4) cells. This isolation of non-cytocidal natural variants of HIV raises the possibility that in some AIDS cases the neurological disorders might be due to HIV variants that are non-cytocidal to T4 cells. The results also indicate that virus replication and cytotoxicity are not always concordant functions in HIV.

Acquired Immunodeficiency Syndrome↗
PubMed1981

Kaposi's sarcoma in homosexual men-a report of eight cases.

The clinical findings in eight young homosexual men in New York with Kaposi's sarcoma showed some unusual features. Unlike the form usually seen in North America and Europe, it affected younger men (4th decade rather than 7th decade); the skin lesions wee generalised rather than being predominantly in the lower limbs, and the disease was more aggressive (survival of less than 20 months rather 8-13 years). All eight had had a variety of sexually transmitted diseases. All those tested for cytomegalovirus antibodies and hepatitis B surface antigen of anti-hepatitis B antibody gave positive results. This unusual occurrence of Kaposi's sarcoma in a population much exposed to sexually transmissible diseases suggests that such exposure may play a role in its pathogenesis.

Adult↗
PubMed1981

Filtration versus gravity leukapheresis in febrile granulocytopenic patients: a randomized prospective trial.

Forty-eight patients with fever greater than 38.3 degrees C for at least 24 hr despite broad spectrum antibiotics and an absolute granulocyte count less than 1000/microliter were randomly allocated to 4 days of granulocyte transfusions obtained by leukapheresis using filtration (n = 27) or gravity (n = 21) techniques, the latter permitting simultaneous nonmechanical collection of granulocytes and platelets utilizing hydroxyethyl starch as a sedimenting agent. Patient characteristics and dose of granulocytes obtained from both techniques were similar. Complete response to granulocyte transfusions was established by a reduction in temperature to less than 37.2 degrees C sustained for at least 48 hr after the fourth transfusion with sterilization of cultures where previously positive and diminution of measurable infection when present. This occurred in 6/21 (29%) for gravity leukapheresis and 9/27 (33%) for filtration leukapheresis. An additional group had diminution in temperature and clinical improvement during transfusions (6/21 gravity leukapheresis versus 10/27 filtration leukapheresis). Eighty-six percent of patients transfused with gravity leukapheresis cells were alive at day 20 compared with 81% for filtration leukapheresis cells. Transfusion reactions were comparable. Thus, gravity leukapheresis appears to be as efficacious as filtration leukapheresis for treating granulocytopenic febrile patients, with the added advantages of availability to any blood bank without new equipment, of having platelets as by-products, and of not requiring donor heparinization.

Adolescent↗
PubMed1976

Red blood cell metabolism in AKR mice in the prelymphomatous phase.

The purpose of this study was to evaluate erythrokinetics and in vitro red blood cell (RBC) glucose utilization, 2,3-diphosphoglycerate production, and adenosine triphosphate levels following incubation in AKR mice from early in life until the onset of AKR lymphoma. Normal BALB/c mice served as controls. While hemoglobin concentration and RBC survival remained constant and similar in both groups of mice, the half disappearance time of injected radioactive 59Fe was longer and the 48-hr reappearance of 59Fe was less in AKR mice, compared with those of BALB/c mice. In vitro RBC metabolic studies indicated increased glucose utilization and 2,3-diphosphoglycerate production and decreased adenosine triphosphate levels following incubation in AKR RBC, in contrast to those in BALB/c RBC. RBC metabolic studies were also done in a small group of low leukemic C3H mice, and were similar to BALB/c mice. These differences became most marked in RBC from mice aged 15 to 30 weeks. Overt lymphoma began to occur after age 40 weeks. Hence, these erythropoietic changes occurred prior to the onset of lymphoma. The data imply a direct effect of virus infection on RBC or their precursors. The results are similar to changes in RBC metabolism noted in Rauscher-infected BALB/c mice. The broader implication of these findings in reference to viral host interactions and human leukemogenesis is discussed.

Adenosine Triphosphate↗