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Biomedical subjects

A C Chan

Publications and source records attributed to A C Chan.

At least 91 records · Page 5Linked to original sources
PubMed1998

Use of preoperative autologous blood donation in liver resections for colorectal metastases.

BACKGROUND: Transfusion of allogeneic blood is associated with risks of human immunodeficiency virus and hepatitis transmission, transfusion reactions, and other potential immunologic and infectious complications. To determine if predonation of autologous blood impacts upon transfusion practice and clinical outcome following liver resection, clinical records of 379 consecutive patients undergoing hepatic resection for metastases of colorectal cancer were identified from the prospective hepatobiliary database and reviewed. METHODS: Of the 379 hepatic resections performed for colorectal metastases between January 1991 and January 1996, 240 (63%) were hepatic lobectomy or trisegmentectomy. Thirty-two percent of patients (123 of 379) agreed to preoperative blood donation (POBD), and their clinical characteristics including age, preoperative hemoglobin, and operative mortality were comparable with those of patients without POBD. Liver resections were carried out using standard vascular inflow and outflow control. Parenchymal transections were performed bluntly with maintenance of low central venous pressure (0 to 5 cm H2O). No vascular isolation or normovolemic hemodilution was used intraoperatively. All erythrocyte transfusions during the entire hospital stay were considered and compared between the two groups. RESULTS: Forty-five percent of patients (172 of 379) received blood transfusions during or after liver resections, of which 61% (105 of 172) required only 1 or 2 units. Only 17% of the POBD group required allogeneic blood. This was significantly less than the group without POBD (43%, P <0.01). There was no significant difference in the operative mortality (2.3% versus 4.9%, P = 0.2) and the median survival (50 versus 40 months, P = 0.3). CONCLUSIONS: Major hepatic resections using current surgical techniques can be performed safely with low blood loss and transfusion is required for only a minority of patients. POBD further reduces transfusion requirement.

Adult↗
PubMed1998

Desmoplastic variant of ameloblastoma in Chinese patients.

Desmoplastic ameloblastoma is a rare tumour, and we know of only 43 previously reported cases. We report seven Chinese patients (five men and two women) with the desmoplastic variant of ameloblastoma, which makes up 9% of all ameloblastomas diagnosed during the years 1981-1995. The age ranged from 18 to 68 years (mean 43). Five of the tumours were in the maxilla and two were in the mandible. Five of them were situated anteriorly, the remaining two cases involving both anterior and posterior maxilla. The features of the 42 cases previously reported were reviewed and were compared with those in the present study. Our results differ in that we found a male predominance, wider age range and more tumours in the maxilla. Histologically, this variant of ameloblastoma is characterized by abundant collagenous stroma. Because the epithelial clusters may show prominent squamous metaplasia or may be compressed into thin strands in most areas, the appearance may mimic a squamous odontogenic tumour or odontogenic fibroma. The behaviour of this variant of ameloblastoma is likely to be the same as that of the classic ameloblastoma.

Adolescent↗
PubMed1998

BLNK: a central linker protein in B cell activation.

Linker or adapter proteins provide mechanisms by which receptors can amplify and regulate downstream effector proteins. We describe here the identification of a novel B cell linker protein, termed BLNK, that interfaces the B cell receptor-associated Syk tyrosine kinase with PLCgamma, the Vav guanine nucleotide exchange factor, and the Grb2 and Nck adapter proteins. Tyrosine phosphorylation of BLNK by Syk provides docking sites for these SH2-containing effector molecules that, in turn, permits the phosphorylation and/or activation of their respective signaling pathways. Hence, BLNK represents a central linker protein that bridges the B cell receptor-associated kinases with a multitude of signaling pathways and may regulate the biologic outcomes of B cell function and development.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Regulation of PAK activation and the T cell cytoskeleton by the linker protein SLP-76.

Tyrosine phosphorylation of linker proteins enables the T cell antigen receptor (TCR)-associated protein tyrosine kinases to phosphorylate and regulate effector molecules that generate second messengers. We demonstrate here that the SLP-76 linker protein interacts with both nck, an adaptor protein, and Vav, a guanine nucleotide exchange factor for Rho-family GTPases. The assembly of this tri-molecular complex permits the activated Rho-family GTPases to regulate target effectors that interact through nck. In turn, assembly of this complex mediates the enzymatic activation of the p21-activated protein kinase 1 and facilitates actin polymerization. Hence, phosphorylation of linker proteins not only bridges the TCR-associated PTK, ZAP-70, with downstream effector proteins, but also provides a scaffold to integrate distinct signaling complexes to regulate T cell function.

Actins↗
PubMed1998

Primary CD30-positive anaplastic large cell lymphoma of the lip.

We report a case of primary CD30-positive anaplastic large cell lymphoma of the lip. While extranodal involvement is not uncommon in Ki-1(CD30) anaplastic large cell lymphoma, this is the first reported case of primary lip involvement. The clinical features and clinical outcome in Ki-1 anaplastic large cell lymphoma are discussed.

Aged↗
PubMed1998

Vitamin E up-regulates arachidonic acid release and phospholipase A2 in megakaryocytes.

The release of arachidonic acid is the rate limiting step in eicosanoid synthesis. In mammalian cells, the release of arachidonic acid is catalyzed by several enzymes. The 85 kDa cytosolic phospholipase A2 (cPLA2) is the key enzyme for the release reaction because of its specific acyl selectivity in phospholipid substrates. We have previously reported that vitamin E enrichment potentiates the arachidonic acid release as well as the spontaneous prostacyclin release in human endothelial cells. In contrast, similar enrichment of diets caused a dose-dependent suppression of platelet thromboxane synthesis. Therefore, the present study was undertaken to determine the effect of vitamin E on arachidonate release and phospholipaseA2 activity in a platelet precursor cell, the MEG-01 megakaryocyte cell line. When these cells were incubated with different concentrations of vitamin E, cellular incorporation was linear with the dosages of this vitamin. Determination of arachidonate release after labeling cells with [3H]-arachidonate showed that vitamin E enrichment caused a dose-dependent increase in ionophore A23187-induced [3H]-arachidonic acid release. Analysis of PLA2 activity showed that activity was detected in the cytosol and this activity was completely abolished by the addition of anti-cPLA2, antibody. Determination of cPLA2 activity demonstrated that vitamin E enrichment caused an increase in enzyme activity. Analysis of cPLA2 protein by Western blot revealed that vitamin E caused an increase in enzyme protein. These data showed that the potentiation of arachidonic acid release and cPLA2, activity by vitamin E was mediated by the enhanced expression of cPLA2 protein.

Arachidonic Acid↗
PubMed1998

Recurrent isolated extramedullary relapses as granulocytic sarcomas following allogeneic bone marrow transplantation for acute myeloid leukemia.

Isolated extramedullary relapses as granulocytic sarcomas (GS) following allogeneic bone marrow transplantation (BMT) for acute myeloid leukemia (AML) are rare events. We describe three such patients who presented with a unique pattern of GS relapse post-BMT. The clinical features included repeated relapses in multiple sites, absence of marrow involvement, and prolonged survival. Fluorescence in situ hybridization (FISH) demonstrated persistence of donor hematopoiesis despite disseminated GS. The findings indicated that a graft-versus-leukemia (GVL) effect might operate more strongly in the marrow than in peripheral sites. Finally, our observations suggest that isolated GS relapses after BMT might be compatible with long survivals, and that in patients with marrow hematopoiesis of donor origin, augmentation of the GVL effect might be of use.

Adult↗
PubMed1998

Primary human herpes virus 6 infection transmitted from donor to recipient through bone marrow infusion.

An 8.5-month-old boy with Wiskott-Aldrich syndrome received a sibling matched bone marrow transplant from his healthy non-identical twin brother. The donor had primary human herpes virus 6 (HHV-6) infection around the time of bone marrow donation. The recipient had hepatitis in the first week and then developed fever and rash on day 18. Skin biopsy was shown to have HHV-6 antigen and his peripheral blood leukocytes were HHV-6 DNA positive. He engrafted on day 18 but the ANC dropped from 5.5 x 10(9)/l (day 23) to 0.48 x 10(9)/l (day 34) with persistent HHV-6 DNAemia. Bone marrow on day 35 was positive for HHV-6 DNA. He was treated with G-CSF and ganciclovir with good response. He later had pneumonitis which was treated empirically with foscarnet, ceftazidime and clarithromycin.

Bone Marrow Transplantation↗
PubMed1998

Isolated extramedullary relapse after allogeneic bone marrow transplantation for chronic myeloid leukemia.

Relapse of chronic myeloid leukemia (CML) as extramedullary granulocytic sarcoma (GS) after allogeneic bone marrow transplantation (BMT) is a rare occurrence. We report two patients who developed spinal GS as the first indication of relapse after allogeneic BMT for CML. In both cases, the marrow was in morphologic and karyotypic remission. However, fluorescence in situ hybridization (FISH) successfully demonstrated the presence of a minor Ph-positive clone in the marrow, as well as an occult clone with an additional Ph chromosome detected in one case. The results indicated a stronger graft-versus-leukemia effect in the marrow than in the peripheral tissues.

Adult↗
PubMed1998

Randomized trial of early versus delayed laparoscopic cholecystectomy for acute cholecystitis.

BACKGROUND: The aim of this prospective randomized study was to define the optimum management between early and delayed laparoscopic cholecystectomy for patients with acute cholecystitis. METHODS: Patients were randomized to receive either early laparoscopic cholecystectomy within 24 h of randomization or initial conservative treatment followed by delayed laparoscopic cholecystectomy 6-8 weeks later. RESULTS: There were 53 patients in the early group and 51 in the delayed group. There was no significant difference in conversion rate (early 21 per cent versus delayed 24 per cent), postoperative analgesic requirement (1 versus 2 doses) and postoperative complications. However, the early group had significantly longer operating time (122.8 versus 106.6 min, P = 0.04) and shorter total hospital stay (7.6 versus 11.6 days, P < 0.001). CONCLUSION: Early laparoscopic cholecystectomy is safe and feasible for acute cholecystitis with the additional benefit of shorter total hospital stay. Apart from a shorter operating time, treating patients with delayed laparoscopic cholecystectomy does not offer additional benefit.

Acute Disease↗
PubMed1998

Common bile duct stones become smaller after endoscopic biliary stenting.

BACKGROUND AND STUDY AIMS: Endoscopic biliary stenting is often used for large or difficult common bile duct (CBD) stones that cannot be extracted at one session. We compared the sizes of the CBD stones after a period of stenting. PATIENTS AND METHODS: Over a 6-year period, a total of 444 patients with large CBD stones (> 2 cm diameter) or difficult CBD stones were managed in our endoscopy unit, of which 46 were treated by endoscopic stenting. Twenty-eight had second ERCP for stone removal after a median period of 63 days (range 17-1002 days). The largest diameter of the stones and the CBD (after correction of magnification) before and after stenting were compared using the Wilcoxon signed test. RESULTS: Before stenting the largest diameters of CBD stones were 11-46 mm (mean 24.9 mm) and decreased to 5-46 mm (mean 20.1 mm) after stenting. The difference in stone sizes was statistically significant although the CBD diameter pre- and post-stenting was not significantly different. The reduction in stone sizes was not significantly correlated with the duration of stenting. CONCLUSION: CBD stones became smaller after stenting. As the difficulty of stone extraction increases with stone size, a period of stenting may make subsequent removal easier for patients with large or difficult CBD stones.

Aged↗
PubMed1998

Detection of trisomy 3 in primary gastric B-cell lymphoma by using chromosome in situ hybridization on paraffin sections.

Recent studies in Western populations have shown that trisomy 3 is the most frequent chromosomal abnormality in primary gastric lymphoma (PGL). To study the incidence of trisomy 3 and its implications for the pathogenesis of PGL in Hong Kong, we have applied the technique of chromosome in situ hybridization in 13 cases of PGL by using archival paraffin-embedded tissue sections. Five cases of chronic gastritis were used as controls. Trisomy 3 was found in 9 (69%) of 13 cases, including cases of low-grade lymphoma and high-grade lymphoma with or without a low-grade component. Our findings are similar to the incidence of trisomy 3 reported in the Western literature. The persistent finding of trisomy 3 in various histologic grades of PGL suggests that it may be useful as a clonal marker in this group of neoplasms. Various molecular events involving chromosome 3 may be related to the pathogenesis of this group of lymphomas.

Chromosomes, Human, Pair 16↗
PubMed1998

Vitamin E and atherosclerosis.

Vitamin E was advocated as an effective treatment for heart disease by Dr. Even Shute of London, Ontario more than 50 years ago. His pioneering claims, which were unacceptable to the medical community at large, have been confirmed by recent findings from epidemiologic studies and clinical trials. This review integrates our current knowledge of atherogenesis with the biological functions of vitamin E. The response-to-injury hypothesis explains atherosclerosis as a chronic inflammatory response to injury of the endothelium, which leads to complex cellular and molecular interactions among cells derived from the endothelium, smooth muscle and several blood cell components. Inflammatory and other stimuli trigger an overproduction of free radicals, which promote peroxidation of lipids in LDL trapped in the subendothelial space. Products of LDL oxidation are bioactive, and they induce endothelial expression and secretion of cytokines, growth factors and several cell surface adhesion molecules. The last-mentioned are capable of recruiting circulating monocytes and T lymphocytes into the intima where monocytes are differentiated into macrophages, the precursor of foam cells. In response to the growth factors and cytokines, smooth muscle cells proliferate in the intima, resulting in the narrowing of the lumen. Oxidized LDL can also inhibit endothelial production of prostacyclin and nitric oxide, two potent autacoids that are vasodilators and inhibitors of platelet aggregation. Evidence is presented that vitamin E is protective against the development of atherosclerosis. Vitamin E enrichment has been shown to retard LDL oxidation, inhibit the proliferation of smooth muscle cells, inhibit platelet adhesion and aggregation, inhibit the expression and function of adhesion molecules, attenuate the synthesis of leukotrienes and potentiate the release of prostacyclin through up-regulating the expression of cytosolic phospholipase A2 and cyclooxygenase. Collectively, these biological functions of vitamin E may account for its protection against the development of atherosclerosis.

Animals↗
PubMed1998

Scrotal skin ulcer in a patient with a previous tonsillectomy because of natural killer cell lymphoma.

The CD56+ lymphomas are a recently characterized high-grade malignancy of putative natural killer cell origin. They are mostly localized to the nasal areas but show a propensity to spread to or recur in the skin. We describe a unique case of CD56+ natural killer lymphoma that recurred in scrotal skin in a patient 8 years after an initial limited resection. Although this case was unusual in showing a prolonged period of apparent remission, it illustrated a characteristic clinicopathologic behavior of this rare tumor.

Genital Neoplasms, Male↗
PubMed1998

Genetic evidence of a role for Lck in T-cell receptor function independent or downstream of ZAP-70/Syk protein tyrosine kinases.

T-cell antigen receptor (TCR) engagement results in sequential activation of the Src protein tyrosine kinases (PTKs) Lck and Fyn and the Syk PTKs, ZAP-70 and Syk. While the Src PTKs mediate the phosphorylation of TCR-associated signaling subunits and the phosphorylation and activation of the Syk PTKs, the lack of a constitutively active Syk PTK has prohibited the analysis of Lck function downstream of these initiating signaling events. We describe here the generation of an activated Syk family PTK by substituting the kinase domain of Syk for the homologous region in ZAP-70 (designated as KS for kinase swap). Expression of the KS chimera resulted in its autophosphorylation, the phosphorylation of cellular proteins, the upregulation of T-cell activation markers, and the induction of interleukin-2 gene synthesis in a TCR-independent fashion. The KS chimera and downstream ZAP-70 or Syk substrates, such as SLP-76, were still phosphorylated when expressed in Lck-deficient JCaM1.6 T cells. However, expression of the KS chimera in JCaM1.6 cells failed to rescue downstream signaling events, demonstrating a functional role for Lck beyond the activation of the ZAP-70 and Syk PTKs. These results indicate that downstream TCR signaling pathways may be differentially regulated by ZAP-70 and Lck PTKs and provide a mechanism by which effector functions may be selectively activated in response to TCR stimulation.

Enzyme Activation↗
PubMed1998

[Expression of cytotoxic-granule-associated protein TIA-1 in nasal NK/T cell lymphomas and lymphoid hyperplasia].

OBJECTIVE: 27 cases of nasal NK/T cell lymphomas were studied for the expression of the cytotoxic-granule-associated protein TIA-1, its immunophenotype, genotype and Epstein-Barr virus infection status. METHODS: Immunohistochemical staining for TIA-1, CD3, CD56, CD45RO, CD8, CD20; polymerase chain reaction (PCR) for TCR gamma chain gene and immunoglobulin JH chain gene rearrangement analysis; in situ hybridization for EBER 1/2 and double staining for TIA-1, CD8 with EBER 1/2. 10 cases of lymphoid hyperplasia were used for comparison. RESULTS: (1) In the 27 cases of nasal NK/T cell lymphomas, most tumor cells expressed TIA-1, CD3, CD45RO and EBER 1/2; expression of CD56 was found in 26 cases; no CD8 or CD20 were detected in tumors cells of this series of cases. Double labelled staining showed that the TIA-1 positive tumor cells coexpress EBER 1/2. TCR gamma chain gene rearrangement was detected in only 1 of the 27 cases. (2) In the 10 cases of lymphoid hyperplasia of nasal pharynx, a small amount of TIA-1 positive cells were present in 8 cases and their distribution similar to that of CD8+ cells, in 4 of these cases a few EBER 1/2+ cells were detected, the number of CD45RO+ cells and CD20+ cells were similar in all 10 cases. Double labelled staining showed that the EBER 1/2+ cells did not coexpress TIA-1. CONCLUSION: A high percentage of these tumor cells express TIA-1 and correlate with that of CD56, CD3 epsilon, CD45RO and EBER1/2 in nasal NK/T cell lymphomas. It is suggested that expression of TIA-1 in this tumor may be related to the tumor origin and may also be responsible for its special biologic behavior.

Adolescent↗