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Biomedical subjects

K Chen

Publications and source records attributed to K Chen.

At least 469 records · Page 26Linked to original sources
PubMed1992

Metastasis-associated alterations in phospholipids and fatty acids of human prostatic adenocarcinoma cell lines.

Metastatic variants of human prostatic adenocarcinoma cell lines (DU-145, LNCaP, and ND-1) were studied by using soft agar colony forming efficiency, nude mice tumorigenicity, in vitro invasion assay, and type IV collagenase assay. The DU-145 and ND-1 cell line showed higher metastatic potential than LNCaP. Lipids from DU-145, ND-1, and LNCaP cells were extracted and analyzed by thin-layer chromatography and gas-liquid chromatography. The major lipids were phosphatidylcholine, phosphatidylethanolamine, sphingomyelin, fatty acids, and cholesterol. The sphingomyelin level was significantly higher in highly metastatic cells (DU-145 and ND-1) compared with the lower metastatic variant (LNCaP). The increase in the synthetic pathway and decrease in degradation pathway of sphingomyelin in microsomal fractions was sufficient to account for the measured increase in sphingomyelin in DU-145 cells compared with LNCaP cells. The major fatty acids of these lipids were palmitic (16:0), stearic (18:0), oelic (18:1), and arachidonic acid (20:4). The arachidonic acid level was significantly decreased in DU-145 and ND-1 compared with LNCaP cells. Electron microscopic studies showed no significant changes in the morphology of DU-145, ND-1, and LNCaP cells. The results of these investigations demonstrate for the first time that sphingomyelin and arachidonic acid contents are different in high and low metastatic variants of human prostatic adenocarcinoma cell lines.

Adenocarcinoma↗
PubMed1992

Stages of progression in drug involvement from adolescence to adulthood: further evidence for the gateway theory.

Sequential stages of involvement in alcohol and/or cigarettes, marijuana, other illicit drugs and medically prescribed psychoactive drugs from adolescence to adulthood are investigated in a longitudinal cohort that has been followed from ages 15 to 35. Alternative models of progression are tested for their goodness of fit. Four stages are identified: that of legal drugs, alcohol or cigarettes; marijuana; illicit drugs other than marijuana; and medically prescribed drugs. Whereas progression to illicit drugs among men is dependent upon prior use of alcohol, among women either cigarettes or alcohol is a sufficient condition for progression to marijuana. Age of onset and frequency of use at a lower stage of drug use are strong predictors of further progression.

Adolescent↗
PubMed1992

Evidence for phase-locking response to hypoxia in peripheral chemoreceptor activity in man.

A number of animal studies have demonstrated that the ventilatory response to stimulation of the peripheral chemoreceptors is well reproduced only when it is stimulated during inspiratory period. In humans, such a response has not been confirmed when using a mild hypoxic stimulus. We, therefore, hypothesized that this response may be detected when a more intense hypoxia is applied. To confirm this hypothesis, six healthy subjects inhaled N2 gas mixture with 5% CO2 in an amount of vital capacity. This procedure started from steady state mild hypoxia (PET02; 60-70 mmHg). Inspiratory and expiratory minute ventilation (VI and VE), tidal volume (VT), and inspiratory and expiratory time (TI and TE) of the breath, at the start of falling oxygen saturation, were analyzed. 21% O2 + 5% CO2 balanced with N2 was inhaled and a breath cycle with a similar latency as during N2 gas mixture inhalation was also analyzed as a control. When oxygen saturation began to drop at the inspiratory phase, the increment of ventilation and tidal volume were larger than the control. When it occurred at the expiratory phase, no significant difference from the control was seen. These results signify the presence of rectification of chemoreceptor afferent signal in humans and may support the concept of oscillation hypothesis as an effective ventilatory stimulus.

Adult↗
PubMed1992

Inflammatory leukocytes associated with increased immunosuppression by glioblastoma.

In order to determine the in vivo immune response in glioblastoma, monoclonal and polyclonal antibodies specific for inflammatory leukocytes and immunoregulatory products were utilized to stain tissue from four surgical specimens. The more activated the inflammatory cells, the more activated the tumors appeared to be. In the tumor with the largest infiltration (Case 3), inflammatory cells were stained for interferon-gamma, interleukin-2, interleukin-1 beta, lymphotoxin, tumor necrosis factor-alpha, and transforming growth factor-beta. The tumor cells also expressed interleukin-1 beta, interleukin-6, transforming growth factor-beta, tumor necrosis factor-alpha, and prostaglandin E. In contrast, in the tumor with the least inflammatory response (Case 1), the tumor cells did not express any cytokines. Expression of cytokines by glioma cells was modest in the two cases with modest inflammatory responses. Cellular inflammation, primarily consisting of T cells and macrophages with few or no B cells or natural killer cells, was two- to 15-fold greater outside the tumor than within. In contrast to leukocytes outside the tumor, which were activated and expressing class II major histocompatibility antigens, leukocytes within the tumor parenchyma or at the tumor's edge were negative for these antigens. In the four specimens studied here, the tumor cells themselves were also negative for class II major histocompatibility antigens. These findings, although preliminary, suggest that inflammatory cells within gliomas are inactivated and that glioma cells may increase the expression of immunosuppressive cytokines in response to an increased lymphocyte infiltrate. This observation, if corroborated by more extensive studies, may help to explain the failure of immune treatments in glioblastoma multiforme.

Adult↗
PubMed1992

[Active life expectancy in Taiwan: compression or expansion?].

"This paper applies the multiple-decrement life table to the analysis of mortality and self-reported disability [for Taiwan], annually from 1986 until 1989.... It was found that during this period of time, the shifts in 'mortality' and 'disability' curves conform to the compression hypothesis. The area in between the two curves [has] shrunk in the 4 year period.... The sex differential in disability has been examined. It is concluded that though at the younger ages women tend to spend less person-years in disability, the situation is quite different at older ages. Women tend to have greater chance [of] and longer duration suffering from disability at old age than men." (SUMMARY IN ENG)

Adult↗
PubMed1992

Ischemic stroke treated with Ligusticum chuanxiong.

Ligusticum Chuanxiong and its effective components were studied in the treatment of ischemic stroke, a common emergent disease in China. Some injections of the medicines, including Ligusticum, Ligustrazine, Ligustylid and ferulic acid, were tested clinically and experimentally. The results showed that the effects of the drugs were the same as or even better than those of the controls, such as papaverine, dextran and aspirin-persantin. They could improve brain microcirculation through inhibiting thrombus formation and platelet aggregation as well as blood viscosity.

Animals↗
PubMed1992

[Isolation and characterization of prolactin messenger RNA from bovine anterior pituitary glands].

The messenger RNA was extracted from bovine anterior pituitary glands and was purified by oligo(dT)-cellulose chromatography. The length of the mRNA was 1,200 nucleotides measured by agarose gel electrophoresis containing methylmercury hydroxide. The bovine prolactin (PRL) mRNA was confirmed by Northern blot analysis of the mRNA with gamma-32P labelled synthetic oligonucleotide probes based on the partial amino acid sequences of bovine PRL and could stimulate the incorporation of 35S-methionine into protein in the rabbit reticulocyte cell-free system. The translation product of bovine PRL mRNA was immunoprecipitable by rabbit anti-ovine PRL anti-antibodies. The molecular weight of the translation product corresponding to the bovine PRL precursor was estimated to be approximately 25,000 by SDS polyacrylamide gel electrophoresis and autoradiograph.

Amino Acid Sequence↗
PubMed1992

Promoter organization and activity of human monoamine oxidase (MAO) A and B genes.

Monoamine oxidase A and B (MAO A and B) play important roles in the metabolism of biogenic and dietary amines and are encoded by two genes derived from a common ancestral gene. The promoter regions for human MAO A and B genes have been characterized using a series of 5' flanking sequences linked to a human growth hormone reporter gene. When these constructs were transfected into NIH3T3, SHSY-5Y, and COS7 cells, the maximal promoter activity for MAO A was found in a 0.14 kilobase (kb) PvuII/DraII fragment (A0.14) and in a 0.15 kb PstI/NaeI fragment (B0.15) for MAO B. Both fragments are GC-rich, contain potential Sp1 binding sites, and are in the region where the MAO A and B 5' flanking sequences share the highest identity (approximately 60%). However, the organization of the transcription elements is distinctly different between these two promoters. Fragment A0.14 consists of three Sp1 elements, all in reversed orientations, and lacks a TATA box. Two of the Sp1 sites are located within the downstream 90 base pair (bp) direct repeat, and the third is located at the 3' end of the upstream 90 bp direct repeat. Fragment B0.15 contains an Sp1-CACCC-Sp1-TATA structure; deletion of any of these elements reduced promoter activity. Additional Sp1 sites, CACCC elements, CCAAT boxes, and direct repeats (four 30 bp direct repeats in MAO A and two 29 bp direct repeats in MAO B) are found in farther-upstream sequences of both genes (1.27 kb for MAO A and mostly in 0.2 kb for MAO B). Inclusion of these sequences decreased promoter activity. The different promoter organization of MAO A and B genes provides the basis for their different tissue- and cell-specific expression.

3T3 Cells↗
PubMed1991

Human monoamine oxidase A and B genes exhibit identical exon-intron organization.

Monoamine oxidases A and B [MAOA and MAOB; amine:oxygen oxidoreductase (deaminating) (flavin-containing), EC 1.4.3.4] play important roles in the metabolism of neuroactive, vasoactive amines and the Parkinsonism-producing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Human MAOA and MAOB genes isolated from X chromosome-specific libraries span at least 60 kilobases, consist of 15 exons, and exhibit identical exon-intron organization. Exon 12 codes for the covalent FAD-binding-site and is the most conserved exon; the MAOA and MAOB exon 12 products share 93.9% peptide identity. These results suggest that MAOA and MAOB are derived from duplication of a common ancestral gene and provide insight on the structural/functional relationship of the enzyme products.

Base Sequence↗
PubMed1991

Reproductive factors and colorectal cancer risk among Chinese females.

We report results from a population-based case-control study of colorectal cancer among Chinese women in western North America (NA) and the People's Republic of China (China). A common protocol was used to assess reproductive characteristics and hormone use of 395 Chinese women (189 from NA and 206 from China) with cancer of the colon or rectum and of 1112 age-matched Chinese controls (494 from NA and 618 from China). In NA, risks for cancers of both the colon and rectum were lower among parous compared to nulliparous women (odds ratio for colorectal cancer, 0.6, P = 0.08), but the trend in risk was not smooth with increasing number of livebirths. This association with parity was absent for both cancer sites in China. There were no consistent patterns in the relationships between other reproductive factors (including age at menarche, age at first livebirth, menopausal status) and risk of colon and rectal cancer on either continent.

Adult↗
PubMed1991

Cellular metabolism of proxyl nitroxides and hydroxylamines.

Previous data from model systems indicated that the proxyl nitroxides should be especially resistant to bioreduction and therefore could be an effective solution to this often problematic characteristic of nitroxides. Therefore, we investigated the rate of reduction by cells and by the usual model system, ascorbate, of four proxyl nitroxides and three reference nitroxides. We found that, while the rate of reduction by ascorbate of the proxyl nitroxides was slower than the rate of a prototypic pyrrolidine nitroxide (PCA), the reverse was true for reduction by cells. We also studied the rate of oxidation of the corresponding hydroxylamines. The rate of oxidation by cells of the proxyl hydroxylamines was relatively fast, especially for the most lipophilic derivative. These results indicate that: (i) proxyl nitroxides may not be unusually resistant to bioreduction by functional biological systems; (ii) accurate knowledge of relative rates of metabolism of nitroxides and hydroxylamines in cells and tissues will require direct studies in these systems because the rates may not closely parallel those observed in model (chemical) systems; and (iii) proxyl nitroxides show potential value as agents to measure oxygen concentrations by the rates of oxidation of their corresponding hydroxylamines.

Animals↗
PubMed1991

Contrast agents for magnetic resonance spectroscopy: a method to obtain increased information in in vivo and in vitro spectroscopy.

The concept of contrast, which now is an integral part of many magnetic resonance imaging studies, can be extended successfully to magnetic resonance spectroscopy. It involves the use of paramagnetic molecules whose distribution is restricted in some manner, thereby causing differential effects on the NMR spectra. As an illustrative example, the effects of lipophilic nitroxide stable free radicals on the NMR spectra of serum and lipoproteins are shown. These nitroxides differentially broaden away components of the spectra due to the nuclei of methylene and methyl groups, which enables the usually obscured peaks of lactate to be observed fully. The concept can be applied to differential distribution of the contrast agent on the basis of solubility, charge, and/or compartmentalization. It can be used with any type of NMR spectroscopy and any type of paramagnetic contrast (broadening) agent.

Animals↗