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Biomedical subjects

W K Chan

Publications and source records attributed to W K Chan.

At least 145 records · Page 8Linked to original sources
PubMed1987

Randomised study of ticarcillin, cefamandole with or without tobramycin in febrile, neutropenic patients with solid tumors.

A prospective randomised study was conducted comparing the efficacy and toxicity of the antibiotics ticarcillin and cefamandole (TC) with or without tobramycin (TCT) in 100 febrile neutropenic patients with solid tumours undergoing conventional chemotherapy. In this study, neutropenia less than 100/microliter was noted in 31% of 106 evaluable infectious episodes and neutrophil counts less than 1,000/microliter persisted for a median 4 days. Infection was microbiologically documented in 42% of episodes (bacteremia 24%) with gram-negative organisms responsible for 63% of bacterial isolates. Overall, 65% of episodes responded to TC and 76% to TCT (p greater than 0.05). Patients with initial shock bacteremia, pulmonary infection, or gram-negative sepsis responded relatively poorly. Neutrophil nadir and pathogen susceptibility did not influence outcome. Antibiotic toxicity was minimal with no tobramycin-related nephrotoxicity. These results are broadly comparable to those observed with leukemic patients, but the relatively short duration of neutropenia in the solid-tumour patients appears to minimize the need for additional antibiotics provided there is adequate antimicrobial coverage with the initial choice of antibiotics.

Adult↗
PubMed1987

Induction of aromatase activity in porcine granulosa cells by FSH and cyclic AMP.

This paper examines the involvement of mRNA and protein synthesis in the induction of aromatase activity by FSH and also the site of action of androgens on FSH induction of aromatase activity in porcine granulosa cells. Treatment of cells with FSH or dbcAMP for an initial 48 h (induction period) resulted in an induction of aromatase activity, as measured by the production of estradiol during a subsequent 6h test period. Addition of testosterone to cells cultured with dbcAMP during the induction period enhanced the aromatase activity during both the induction and test periods. However, while DHT has no effect during the induction period, it significantly inhibited the aromatase activity during the test period. Culturing the granulosa cells with actinomycin D or cycloheximide during the induction period resulted in a dose-dependent inhibition of FSH induction of aromatase activity, suggestive of the synthesis of new protein(s). These results indicate clearly that FSH induction of aromatase activity involves the synthesis of mRNA and proteins.

1-Methyl-3-isobutylxanthine↗
PubMed1987

The cellular secretory pathway is not utilized for biosynthesis, modification, or intracellular transport of the simian virus 40 large tumor antigen.

Unlike most proteins, which are localized within a single subcellular compartment in the eucaryotic cell, the simian virus 40 (SV40) large tumor antigen (T-ag) is associated with both the nucleus and the plasma membrane. Current knowledge of protein processing would predict a role for the secretory pathway in the biosynthesis and transport of at least a subpopulation of T-ag to account for certain of its chemical modifications and for its ability to reach the cell surface. We have examined this prediction by using in vitro translation and translocation experiments. Preliminary experiments established that translation of T-ag was detectable with as little as 0.1 microgram of the total cytoplasmic RNA from SV40-infected cells. Therefore, by using a 100-fold excess of this RNA, the sensitivity of the assays was above the limits necessary to detect the theoretical fraction of RNA equivalent to the subpopulation of plasma-membrane-associated T-ag (2 to 5% of total T-ag). In contrast to a control rotavirus glycoprotein, the electrophoretic mobility of T-ag was not changed by the addition of microsomal vesicles to the in vitro translation mixture. Furthermore, T-ag did not undergo translocation in the presence of microsomal vesicles, as evidenced by its sensitivity to trypsin treatment and its absence in the purified vesicles. Identical results were obtained with either cytoplasmic RNA from SV40-infected cells or SV40 early RNA transcribed in vitro from a recombinant plasmid containing the SP6 promoter. SV40 early mRNA in infected cells was detected in association with free, but not with membrane-bound, polyribosomes. Finally, monensin, an inhibitor of Golgi function, failed to specifically prevent either glycosylation or cell surface expression of T-ag, although it did depress overall protein synthesis in TC-7 cells. We conclude from these observations that the constituent organelles of the secretory pathway are not involved in the biosynthesis, modification, or intracellular transport of T-ag. The initial step in the pathway of T-ag biosynthesis appears to be translation on free cytoplasmic polyribosomes. With the exclusion of the secretory pathway, we suggest that T-ag glycosylation, palmitylation, and transport to the plasma membrane are accomplished by previously unrecognized cellular mechanisms.

Animals↗
PubMed1987

Synthesis and immunogenicity of the rotavirus major capsid antigen using a baculovirus expression system.

Rotaviruses are the major pathogens that cause life-threatening diarrhea in young children and animals. We inserted a simian rotavirus SA11 gene 6 cDNA into the genome of the baculovirus Autographa californica nuclear polyhedrosis virus adjacent to the strong polyhedrin promoter. The major capsid antigen (VP6) was expressed in high yields (20 to 150 micrograms/10(6) cells) when Spodoptera frugiperda cells were infected with baculovirus recombinants containing SA11 gene 6 inserts. Reactivity with monospecific polyclonal and monoclonal antibodies suggested that VP6, expressed intracellularly or found in the media, maintained native antigenic determinants. VP6 purified from the media from infected cells also possessed a native oligomeric structure, was immunogenic in guinea pigs, and was able to spontaneously assemble into morphologic subunits. Antisera from immunized guinea pigs failed to neutralize virus in plaque reduction assays, but detected homologous and heterologous rotavirus strains when tested by immunofluorescence, immunoprecipitation, and enzyme-linked immunosorbent assays.

Antibodies, Viral↗
PubMed1986

Two glycoproteins are produced from the rotavirus neutralization gene.

The major neutralization antigen of rotaviruses is an outer capsid glycoprotein, VP7, with an apparent molecular weight of 38,000 (38K). The simian rotavirus SA11 genome segment 9, which codes for VP7, contains two in-phase initiation codons, each of which is followed by a sequence that codes for a region of hydrophobic amino acids. We have determined that this gene is functionally bicistronic by analyzing the synthesis of VP7 in SA11-infected cells and in cell-free translation systems programmed with hybrid-selected, segment 9 specific mRNA and dog pancreatic microsomes. The translation of hybrid-selected gene 9 mRNA in wheat germ extracts yielded two distinct polypeptides of molecular weights 37K and 35.3K. In vitro translation in the presence of microsomes yielded one diffuse band of 38K that was converted into the 37K and 35.3K precursor bands by digestion with endoglycosidase H. Studies with a variant of SA11 that lacks the glycosylation site in VP7 confirmed these precursor-product relationships and extended them by indicating that the glycoprotein produced by translation from the first AUG contained a cleaved signal sequence whereas the glycoprotein produced by translation from the second AUG contained an uncleaved signal sequence. Immunoprecipitation with monospecific anti-VP7 serum and improved gel electrophoresis conditions allowed us to show that both VP7s were expressed at similar times in infected cells and both were found in purified virus particles of several different rotavirus strains. Whether these two VP7 glycoproteins are functionally distinct remains to be determined.

Antigens, Viral↗
PubMed1986

Inhibition of follicle-stimulating hormone induction of aromatase activity in porcine granulosa cells by thyroxine and triiodothyronine.

We examined the effects of T3 and T4 on basal and FSH-induced aromatase activity in granulosa cells isolated from medium-sized follicles (4-6 mm) of prepubertal pigs. Treatment of cells with T3 or T4 alone during an initial 48-h induction period did not result in any significant change in aromatase activity, as measured by 17 beta-estradiol accumulation during the subsequent 6-h test period, when testosterone (0.5 microM) was added as substrate. However, when cells were cultured with FSH and T3 or T4 during the induction period, a definite dose-dependent inhibition of FSH-induced aromatase activity was demonstrated. This inhibition was not altered by the presence of a binding protein (BSA). The inhibition of FSH-induced aromatase activity by T4 and T3 is a true biological effect, as inactive iodocompounds (MIT and DIT) and iodide had no significant effect on the gonadotropin-induced aromatase activity. Furthermore, the viability of cells was unaffected by the thyroid hormones, and total cellular protein did not change significantly. These results indicate that thyroid hormones might play an important role in modulating FSH-induced aromatase activity, and that the elevated plasma estrogen levels in some cases of hyperthyroidism are not due to increased ovarian secretion.

Animals↗
PubMed1986

FSH-induced aromatase activity in porcine granulosa cells: non-competitive inhibition by non-aromatizable androgens.

The aim of this study was to examine the inhibitory effect of the non-aromatizable androgens on FSH-stimulated aromatase activity in porcine granulosa cells. The cells were isolated from medium-sized follicles (4-6 mm) of prepubertal pigs, and cultured under chemically defined conditions in the presence of FSH (1 microgram/ml, NIADDK-oFSH-S13) with and without the androgens for an initial 48-h induction period. Subsequently, the spent medium was replaced with fresh medium containing only testosterone as substrate and the cells were reincubated for a further 6 h. The conversion of this steroid to oestradiol-17 beta during this latter 'test' period was taken as a measure of the aromatase activity. The addition of 5 alpha-dihydrotestosterone (DHT) into cultures of FSH-stimulated cells during the induction period resulted in a definite dose-dependent inhibition (30-70%) of the aromatase activity expressed in the test period. This inhibitory action, of the mixed non-competitive type, is characterized by a decrease in the apparent Vmax and an increase in the Km value, suggestive of an androgen inhibition of FSH-stimulated aromatase synthesis. This inhibition was also shown by the other 5 alpha- and 5 beta-reduced androgens: 5 beta-androstanedione was the most effective, while DHT was the least. Other steroids such as pregnenolone and progesterone were inhibitory, but testosterone and diethylstilboestrol were stimulatory. These results suggest an important mechanism for the intrafollicular control of oestrogen synthesis, involving a possible reciprocal relationship between aromatase and 5 alpha-reductase activities.

Animals↗
PubMed1983

Fast diffusion along defects and corrugations in phospholipid P beta, liquid crystals.

The diffusion of a fluorescent lipid analogue in liquid crystals of the anisotropic P beta, phase of dimyristoylphosphatidylcholine (DMPC) had been found to be highly variable, suggesting structural defect pathways. Fluorescence photobleaching recovery (FPR) experiments imply two effective diffusion pathways with coefficients differing by at least 100. This is consistent with fast diffusion along submicroscopic bands of disordered material ("defects") in the bilayer corrugations characteristic of this phase. Due to strains during transformation from the L alpha phase, the axis of the corrugations is ordinarily disrupted by mosaic patches rotationally disoriented within the mean plane of the molecular bilayers, although larger oriented domains are sometimes adventitiously aligned into microscopically visible striped textures. The corrugations are also systematically aligned along positive disclinations pairs or "oily streaks." Thus, fast diffusion occurs parallel to the disclination lines and along the textured stripes. FPR results yield an upper limit on the effective diffusion in the ordered material of D less than or equal to 2 X 10(-16) cm2/s at 22 degrees C, D less than or equal to 3 X 10(-17) cm2/s at 13 degrees C. In contrast the diffusion coefficient along defect pathways where disordered ribbons are aligned is D approximately 4 X 10(-11) cm2/s at 16 degrees C.

Crystallization↗
PubMed1982

Four-drug combination chemotherapy for advanced cervical carcinoma.

Thirty-one patients with advanced stage squamous cell carcinoma of the cervix were treated with the four-drug combination fluorouracil, doxorubicin, cyclophosphamide, and vincristine. Four patients achieved complete remission (13%) and 15 partial remission (45%). The only factor of adverse prognostic significance was poor initial patient performance. Median survival for the patients entering complete remission exceeded 54 weeks and was 43 weeks for patients achieving partial remission. Seven patients are still alive at 50 weeks. This represents a notable prolongation of survival compared with those patients who did not achieve remission. Toxicity for the combination was not excessive; myelosuppression and vincristine-induced neuropathy were the most prominent. These results are moderately encouraging and confirm the sensitivity of cervical carcinoma to systemic chemotherapy. Further studies to define the optimal use of chemotherapy in both advanced and earlier stages of disease are warranted.

Adult↗
PubMed1982

Alternating non-cross-resistant combination chemotherapy for small cell anaplastic carcinoma of the lung.

The development of drug resistance limits the survival or patients with small cell anaplastic carcinoma of the lung (SCLC). The present study was undertaken to overcome this problem by administering two alternating noncross resistant combination chemotherapy regimens. One-hundred-one patients were entered on study, and 98 were evaluable, with a median onstudy time of 55+ weeks. All patients received the initial combination therapy of cyclophosphamide, methotrexate, and vincristine, alternating every three weeks with Adriamycin and VP16-213 (etoposide). Radiation therapy was not a standard part of protocol. Thirty-two patients had regional disease (LD), and 66 had extensive disease (ED). Overall, 76% of patients responded to this therapy with 30 (31%) complete remission (CR) and 44 (45%) partial remissions (PR); the respective CR and PR rates were 31% and 50% for LD, and 30% and 42% for ED patients. Myelosuppression was the principal toxicity with a leukocyte nadir of 2.0 X 10(9)/1 in 10% of cycles. Septicemia in six neutropenic ED patients with progressive disease contributed to the only treatment-related deaths. Patients entering CR had a median survival greater than 51 weeks (range, 8-150+); 58+ for LD and 49+ for ED patients. Patients in PR had respective median survivals of 33+ (overall), 43+ (LD), and 24+ (ED) weeks. Forty patients have had relapses with initial sites being local sites in 35%, and neurologic in 38%. Although this protocol has not discernibly delayed the onset of drug resistance, the problem should be considered when new protocols are designed in SCLC.

Antineoplastic Agents↗
PubMed1981

Methyl-CCNU, 6-thioguanine, and 5-fluorouracil in advanced colorectal cancer.

Consecutive studies were undertaken in advanced colorectal adenocarcinoma, comparing two different schedules of the combination methyl-CCNU, 6-thioguanine, and 5-fluorouracil in 89 patients. The two schedules exhibited similar efficacies, with a combined complete and partial remission rate of 17%, a median response duration of 36+ weeks, and a median survival of 53+ weeks. Significant symptomatic benefit was seen in 52% of patients. Toxicity was predominantly hemopoietic and gastrointestinal, being acceptable overall, with only minor qualitative differences between the two protocols. These triple-drug regimens exhibit response rates and survival patterns comparable with those reported for other multidrug combinations and some single agents. It would appear that major improvements in the management of advanced-stage disease must await the availability of more efficacious agents used alone or in combination.

Adenocarcinoma↗
PubMed1981

Meningeal carcinomatosis in small cell carcinoma of the lung.

Cerebral and meningeal metastases are increasingly important complications in small cell anaplastic carcinoma of the lung. In a study at this institution, 60 evaluable patients received intensive chemotherapy without prophylactic cranial irradiation or other prophylactic measures. The complete plus partial remission rate was 78 percent with a median survival of 49+ weeks (range eight to 106+ weeks) for those with a complete response and 18+ weeks (range six to 67 weeks) for those with a partial response, all of which are comparable to other reported series. In 11 patients (18 percent) meningeal carcinomatosis has developed. Forty-two percent of the patients with a relapse have exhibited meningeal carcinomatosis and in 27 percent of the patients with a relapse it was the only site of relapse. Cerebral metastases occurred in 27 percent of those who had a relapse, and in 12 percent this was the sole site of relapse. Simultaneous meningeal carcinomatosis and cerebral metastases occurred in 8 percent of the patients with a relapse. The median time to meningeal relapse was 27 weeks (range 12 to 60 weeks) compared with 25+ weeks (six to 106+ weeks) over-all, and the median survival was 28 weeks (range 14 to 82 weeks) compared with 25+ weeks (two to 106+ weeks) for the whole group with small cell carcinoma of the lung. Meningeal involvement in small cell carcinoma of the lung must now be considered a sanctuary site of equal importance to cerebral metastases. To prevent and treat this complication will necessitate evaluation of all available modalities, including cranial and spinal irradiation, intrathecal chemotherapy and systemic agents that readily cross the blood-brain barrier.

Adult↗
PubMed1979

Industrial development and health in Malaysia.

Industrial development in Malaysia is discussed in relation to impact on health. Trends in Malaysia are evaluated and the findings of some studies in Malaysia are reviewed.

Accidents, Occupational↗
PubMed1978

Water and hermal diffusivity in a lipid-water smectic phase.

We report the first application of light scattering to measurement of the hydrodynamic relaxation of inhomogeneities in water concentration within a multilamellar, or smectic A, phospholipid water system (dipalmitoyl) phosphatidyl choline). Although the relaxation process in the multilamellar phase is different from the diffusion process in liquid phases, the relaxation rate can be described in terms of a diffusion coefficient. For diffusion parallel to the lamellae, diffusion coefficients ranging from 8 x 10(-7) to 2 x 10(-5) cm2/s were measured over a range of temperature and water concentrations. We describe a model that expresses the diffusion coefficient in terms of the chemical potential for water inside the multilamellar phase and the effective thickness of a "free water zone." The deduced thickness of this free water zone is in good agreement with estimates from X-ray diffraction results. The activation energy for the diffusion process is also deduced from the data, and is found to decrease monotonically with increasing water concentration. We also found the thermal diffusivity to be about 10(-3) cm2/s with only a weak temperature and water concentration dependence. The experimental technique is a new version of forced Rayleigh scattering. The method uses the phase information of the scattered light to improve the ability to detect weak signals. Experimental details are reported.

Diffusion↗