Biomedical subjects

M Chen

Publications and source records attributed to M Chen.

At least 721 records · Page 40Linked to original sources

PubMed1993

5-HT and cAMP induce the formation of coated pits and vesicles and increase the expression of clathrin light chain in sensory neurons of aplysia.

In the course of studying proteins involved in long-term facilitation in Aplysia, we found that 5-HT and cAMP, a second messenger activated by 5-HT, lead to the removal of a set of N-CAM-related cell adhesion molecules (apCAMs) from the surface membrane of sensory neurons by means of receptor-mediated endocytosis. Here we describe that, as part of this coordinated program for endocytosis, 5-HT and cAMP also induce in the sensory neurons an increase in the density of coated pits and coated vesicles and an increase in the expression of the light chain of Aplysia clathrin (apClathrin). The clathrin-related endocytosis seems designed to internalize and redistribute apCAMs and other surface membrane proteins in the sensory neurons, and thus it appears to constitute one of the initial steps in the growth of new synaptic connections that accompanies long-term facilitation.

1-Methyl-3-isobutylxanthine↗

PubMed1993

Long term infection of the gastric mucosa with Helicobacter species does induce atrophic gastritis in an animal model of Helicobacter pylori infection.

Gastric atrophy is a precursor lesion in the development of gastric cancer. It has been proposed that atrophy is part of a natural progression of inflammatory changes that result from long term infection with the bacterium Helicobacter pylori. The aim of this study was to test this hypothesis using an animal model of human Helicobacter infection. Conventional mice were infected with either a cat isolate of Helicobacter felis or a human isolate of "Gastrospirillum hominis". All infected mice showed a slowly progressive chronic gastritis with increasing numbers of infiltrating mononuclear cells and polymorphonuclear leucocytes. After a year and a half, the inflammatory reaction was so severe that atrophic changes were seen in both the antral and fundic mucosa. Control animals initially showed no inflammatory changes however as the animals aged, the gastric mucosa of some animals became infected with a bacterium Helicobacter muridarum that normally inhabits the small and large bowel of the rodent. The presence of this bacterium was also associated with gastritis and atrophic changes. This is the first report of experimentally induced atrophic changes induced by a gastric bacterium and opens the way for important experiments that will help better understand the induction of gastric cancer.

Animals↗

PubMed1993

Immunisation against gastric infection with Helicobacter species: first step in the prophylaxis of gastric cancer?

The discovery of the gastric bacterium, Helicobacter pylori and the demonstration of its role in the pathogenesis of gastroduodenal disease, has been one of the major microbiological advances in the last decade. Recent demonstration of long term infection with this bacterium as a risk factor in gastric carcinoma suggests that intervention in a disease of major morbidity and mortality is possible. Using a model of Helicobacter infection in mice it has been shown that oral immunisation with a sonicate of Helicobacter felis plus the adjuvant cholera toxin results in protection against an oral challenge with large numbers of viable bacteria. The success of the immunising regimen has been shown to correlate with the development of local immunity. Formulation of equivalent safe vaccines of H. pylori will make possible the immunisation of children in countries such as China, Japan and Columbia and so prevent the establishment of long term inflammation and thus significantly reduce the incidence of gastric cancer in those societies. This animal model is proposed as a major tool in the development of effective oral immunisation.

Animals↗

PubMed1993

Flunarizine blocks elevation of free cytosolic calcium in synaptosomes following sustained depolarization.

Gerbil cerebral cortical synaptosomes loaded with the fluorescent calcium probe FURA-2 were used to study depolarization-induced presynaptic cytosolic free calcium concentration, as an in vitro model of cerebral ischemia. The depolarization-induced increase in intrasynaptosomal cytosolic free calcium concentration is not sodium-dependent or sodium channel-dependent and may be due to an influx of extrasynaptosomal calcium resulting from a cadmium- and omega-conotoxin-sensitive, nickel-, nifedipine-, and nimodipine-insensitive voltage-regulated channel. The depolarization-induced increase in intrasynaptosomal free cytosolic calcium concentration is also inhibited by flunarizine, a calcium antagonist that has protective effects in animal models of cerebral anoxia and ischemia. Our results suggest that presynaptic calcium uptake following depolarization may be mediated in part by an N-type channel. Flunarizine may block presynaptic calcium accumulation, in part, by blocking this N-type channel; this blockade may be just one of several mechanisms by which flunarizine exerts protective effects following cerebral ischemia.

Animals↗

PubMed1993

Licochalcone A, a novel antiparasitic agent with potent activity against human pathogenic protozoan species of Leishmania.

Licochalcone A, an oxygenated chalcone isolated from the roots of Chinese licorice plant, inhibited the growth of both Leishmania major and Leishmania donovani promastigotes and amastigotes. The structure of the licochalcone A was established by mass and nuclear magnetic resonance spectroscopies and by synthesis, and its purity was verified by high-pressure liquid chromatography. The 50% inhibition of growth of logarithmic- and stationary-phase promastigotes of L. major, as measured by [3H]thymidine uptake, were 4 and 2.5 micrograms/ml, respectively. The growth of L. major promastigotes was totally inhibited after a 20-h incubation period with licochalcone A at 5 micrograms/ml. At a concentration of 0.5 microgram/ml, licochalcone A markedly reduced the infection rate of human peripheral blood monocyte-derived macrophages and U937 cells with L. major promastigotes and exhibited a strong intracellular killing of the parasite. These data show that intracellular Leishmania amastigotes are more susceptible than promastigotes to licochalcone A. Results of studies on the site of action of licochalcone A indicate that the target organelle appears to be the parasite mitochondria. These findings demonstrate that licochalcone A in concentrations that are nontoxic to host cells exhibits a strong antileishmanial activity and that appropriate substituted chalcones might be a new class of antileishmanial drugs.

Animals↗

PubMed1993

Secretion of streptavidin from Bacillus subtilis.

Streptavidin is an extracellular tetrameric protein produced by Streptomyces avidinii. A series of hybrid gene fusions consisting of Bacillus signal peptide coding regions fused to the mature streptavidin sequence were constructed. B. subtilis strains harboring these plasmids accumulate a tetrameric streptavidin in the growth medium. The properties of the streptavidin produced by B. subtilis are similar to those of the streptavidin produced by S. avidinii. B. subtilis strains carrying the various fusions can be grown to a high cell density in a biotin-free medium. Thus, B. subtilis represents an alternate host system for the production of streptavidin.

Amino Acid Sequence↗

PubMed1993

Serologic analysis of dogs, horses, and cottontail rabbits for antibodies to an antigenic flagellar epitope of Borrelia burgdorferi.

Enzyme-linked immunosorbent assays (ELISA) and immunoblots using either whole-cell lysates of Borrelia burgdorferi or an antigenic region of flagellin (41-G) as the antigen were performed, and the abilities of the two assays to detect antibodies to this spirochete in dog, cottontail rabbit, and horse sera were compared. Assays using whole-cell B. burgdorferi lysates as the antigen were more sensitive for detecting antibodies. ELISA with 41-G as the antigen were specific for Borrelia antibodies but were not as sensitive as the assays with whole-cell lysates coated to the solid phase. Use of recombinant full-length flagellin, rather than 41-G, as the antigen in immunoblots increased the sensitivity of each assay. However, antibodies to other bacterial antigens cross-react with whole flagellin and may account for false-positive results. Antibodies to B. burgdorferi outer surface protein A or B were usually undetected when the sera were tested by immunoblotting methods. Borrelia lysates or the 41-G antigen may be used in ELISA or immunoblots to document host exposure to this spirochete. The use of 41-G as the antigen may increase the specificity of an assay or help confirm the serologic diagnosis of Lyme borreliosis in dogs, horses, and cottontail rabbits.

Animals↗

PubMed1993

Hepatocyte-specific expression of the hepatitis B virus core promoter depends on both positive and negative regulation.

The core promoter of hepatitis B virus shows hepatocyte specificity, which is largely dependent on an upstream regulatory sequence that overlaps with viral enhancer II. Footprint analyses by numerous groups have shown binding by cellular proteins over a large stretch of DNA in this region, but the identity of these proteins and their role in core promoter function remain largely unknown. We present data showing that the transcription factor HNF-4 is one such factor, as it activates the core promoter approximately 20-fold via a binding site within the upstream regulatory sequence. Since HNF-4 is enriched in hepatocytes, its involvement at least partially explains the hepatocyte specificity of this promoter. In addition, however, we have found a region upstream of the HNF-4 site that suppresses activation by HNF-4 in HeLa cells but not in hepatoma cells. Therefore, the cell type specificity of the core promoter appears to result from a combination of activation by one or more factors specifically enriched in hepatocytes and repression by some other factor(s) present in nonhepatocytes, and it may provide a convenient model system for studying this type of tissue-specific transcriptional regulation in mammalian cells.

Base Sequence↗

PubMed1993

Endothelin-1 mRNA in glomerular and epithelial cells of kidney.

To examine the question of the tubular localization of renal endothelin-1 (ET-1) mRNA, cDNA generated by reverse transcription of isolated rat tubule RNA was amplified by polymerase chain reaction using rat ET-1-specific oligonucleotides. Product identity was determined by restriction enzyme digestion or direct product sequencing. ET-1 mRNA was found to increase in renal tissue in a corticomedullary direction. High levels of ET-1 mRNA were found in dissected glomeruli and in juxtaglomerular cells in short-term primary culture. Among tubule segments, ET-1 mRNA was most abundant in inner medullary collecting ducts (IMCD), but products were also found with cDNA derived from proximal convoluted and straight tubules, thick ascending limbs, and outer medullary collecting ducts. In kidneys of untreated, homozygous Brattleboro rats, the increase of ET-1 mRNA along the corticomedullary axis as well as the preponderance of tubular ET-1 mRNA in IMCD was not observed. Our data show that ET-1 mRNA is present in all nephron segments studied and that its expression may be dependent on the functional state of the kidney. Our results are consistent with the proposal that ET-1 modifies tubular function in an autocrine or paracrine fashion.

Animals↗

PubMed1993

Effect of timing of growth hormone administration on plasma growth-hormone-binding activity, insulin-like growth factor-I and growth in children with a subnormal spontaneous secretion of growth hormone.

Since normal pulsatile growth-hormone (GH) secretion displays a major and consistent surge during sleep, we studied the effect of timing of GH supplementation on plasma GH-binding protein activity (GH-BP), insulin-like growth factor-I (IGF-I) and growth. 34 prepubertal subjects (28 boys, 6 girls) aged 8-11 years, of short stature (< 2 SD for age), with a GH response to provocative test > 10 micrograms/l and a subnormal 24-hour GH secretion (< 3 micrograms/l), were randomly allocated to receive Bio-Tropin (recombinant GH, Bio-Technology, Israel) 0.81 IU/kg/week in 3 equally divided doses. GH was administered either at 8.00-10.00 h (M group), 14.00-16.00 h (AN group) or 19.00-21.00 h (NT group). Height velocity, IGF-I and GH-BP were determined prior to and after 6 and 12 months on GH therapy in the three groups. There was no significant difference between the three groups in the growth response, IGF-I and GH-BP increase, all of which increased significantly during GH therapy. Although GH levels after the injection decline to preinjection levels after 10 h, the changes induced by GH therapy, as reflected in IGF-I and GH-BP, last in the circulation long enough to prevent fluctuations in its action. The similarity of IGF-I and of GH-BP levels in the three treatment groups might explain the similar growth effects of the 3 protocols.

Carrier Proteins↗

PubMed1993

The effect of exogenous and endogenous growth hormone on plasma growth hormone binding activity in prepubertal children.

To investigate the relationship between plasma growth hormone (GH) and plasma GH-binding protein (GHBP) activity we studied the effects of exogenous and endogenous GH on GHBP in children with a normal response to GH stimulation. The effect of exogenous GH on plasma binding activity was studied for 12 h after the administration of a subcutaneous GH bolus of 0.1 IU/kg and during the first year of GH therapy. The effect of endogenous GH secretion on GHBP was studied by measuring the integrated concentration (IC) of GH and GHBP over 24 h by means of a continuous blood withdrawal procedure. We also measured the GH and GHBP response to GH provocative tests. One hundred and two prepubertal children, 69 males, 33 females, age 8.8 +/- 2.2 years (mean +/- SD), were studied. Eighty-one were short, < 2 SDS for age and gender, and 21 were of normal height for age and gender. There was no difference in IC-GHBP between boys and girls. It correlated positively with age and body mass index (r = 0.802, p < 0.001 and r = 0.340, p < 0.001, respectively) but correlated negatively with ICGH (r = -0.412, p < 0.001) and with height velocity standard deviation scores (SDS, r = -0.355, p = 0.001). No correlation of ICGHBP with maximal GH response to provocative tests, insulin-like growth factor 1 levels, height in SDS or growth velocity after 1 year of GH therapy was found. During a provocative test there is an abrupt increase in GH but not change in GHBP.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrier Proteins↗

PubMed1993

Time course of stimulation of renal renin messenger RNA by furosemide.

Renin secretion responds rapidly to a variety of stimuli; however, reported changes in renal renin messenger RNA (mRNA) levels in vivo have been observed only after prolonged stimulation. Studies were designed to test whether rapid changes in renin mRNA levels can be produced in vivo. In the first series, Sprague-Dawley rats received furosemide (10 mg/kg) intraperitoneally and a low sodium diet (0.05% sodium); renin secretion was significantly stimulated at 8 or 16 hours after treatment, but renin mRNA levels did not change. In a second series, rats were pretreated with deoxycorticosterone acetate (200 mg/kg) and saline drinking water for 3 days and then killed 0, 2, 4, 8, or 48 hours after furosemide administration. The renin mRNA level was unchanged at 2 hours but was stimulated twofold at 4 and 8 hours and threefold at 48 hours. In additional animals, the response of renin mRNA 4 hours after furosemide was found not to be potentiated by the converting enzyme inhibitor quinapril (5 mg/kg). The results demonstrate that with acute stimulation, renin mRNA levels lag 2-4 hours behind the change in plasma renin levels.

Actins↗

PubMed1993

A receptor for cathepsin G:alpha 1-antichymotrypsin complexes on mouse spinal cord astrocytes.

To determine whether there is a specific receptor for serpin:protease complexes on the astrocyte cell surface, we analyzed the cell-binding characteristics of an 125I-cathepsin G:alpha 1-antichymotrypsin complex. Complex formation is maximal at a 1:1 molar ratio of cathepsin G to alpha 1-antichymotrypsin (alpha 1-ACT) as revealed by sodium dodecyl sulfate-gel electrophoresis and autoradiography. Complex binding to mouse spinal cord astrocytes was inhibited by the presence of excess unlabeled complex, but not by the native protease, cathepsin G, or by the serpin, alpha 1-ACT. Scatchard analysis of the binding curve showed the Kd to be 8 x 10(-8) M. We estimated receptor numbers on astrocytes to be about 2.2 x 10(6) sites per cell. An alpha 1-ACT-derived pentapeptide, Phe-Leu-Met-Ile-Ile (FLMII), homologous to a well-conserved segment in the serpin superfamily, did not inhibit the binding of complexes to cells. These data indicate that a specific receptor for alpha 1-ACT:cathepsin G exists on the CNS glial cell surface. Study of this receptor in astrocytes should facilitate understanding of the serpin:protease balance in the brain.

Animals↗

PubMed1993

Mapping of the 70 kDa, 34 kDa, and 11 kDa subunit genes of the human multimeric single-stranded DNA binding protein (hSSB/RPA) to chromosome bands 17p13, 1p35-p36.1, and 7p21-p22.

Human single-stranded DNA binding protein (hSSB/RPA) is a multimeric single-stranded DNA binding protein consisting of three subunits of 70 kDa, 34 kDa, and 11 kDa. Human SSB was isolated from HeLa cells as an essential factor for the in vitro replication of simian virus 40 DNA. We and others have isolated and sequenced cDNAs for each subunit of the SSB. The chromosome on which each gene is located was determined through the analysis of a panel of human/hamster somatic cell hybrids using the polymerase chain reaction with pairs of synthetic oligonucleotide primers from the 3'-untranslated sequences of the genes. Genomic clones for each gene were isolated from a genomic cosmid library prepared from human lymphoblastoid cells. Using those clones as probes, we have carried out fluorescence in situ hybridization to human metaphase chromosomes and have mapped the 70 kDa subunit gene to 17p13, the 34 kDa subunit gene to 1p35-p36.1, and the 11 kDa subunit gene to 7p21-p22. Since hSSB participates in replication, recombination and repair of DNA, the physical mapping of hSSB genes may aid in the identification of human hereditary diseases associated with aberrant DNA reactions caused by genetic alterations of the hSSB.

Animals↗

PubMed1993

[The relation between protective effect of moxibustion on gastric mucosa and mucus].

Our previous works have proved that moxibustion at "ShenJue" plays a role in protecting gastric mucosa in the experimental gastric ulcer model rat. The present studies are designed to determine whether the mechanisms of moxibustion protecting gastric mucosa are mediated by mucus. The results are as follows: Either before or after the experimental gastric ulcer model had formed, moxibustion treatment would markedly increase the ratio of PAS positive staining layer to total length of gastric gland (p < 0.05), and the combined gastric mucus of stomach (P < 0.05). These results are negatively correlated to gastric ulcer area and suggest that the mechanisms of moxibustion protection on gastric mucosa are mediated by mucus in the experimental gastric ulcer model rat.

Animals↗

PubMed1993

[Effect of targeting treatment of mitomycin C immunoconjugate on stomach neoplasm].

An anti-gastric cancer monoclonal antibody MGb2-mitomycin C conjugate via dextran T-70 as intermediate (MGb2-PAD-MMC) was produced, and 28-30 g molecules of MMC were introduced into 1 g molecule of MGb2. Ninety-six hours after ip of 125I-MGb2-PAD-MMC (1.48 MBq/22 micrograms MGb2 per mouse) to nude mice bearing human gastric cancer SGC-7901, the tumor tissue:blood (T/NT) radioactivity ratio was 2.6, very much higher than that of the control 125I-normal IgG-PAD-MMC group (T/NT = 0.20). Single photo computed tomography imaging confirmed the results of biodistribution study. MGb2-PAD-MMC exhibited selective killing action on the SGC-7901 cells in vitro, which was considered to be mediated by monoclonal antibody MGb2. Nude mice inoculated with SGC-7901 xenograft in bilateral subrenal capsule were treated by MMC (ip), human recombinant interferon-alpha (Hu-IFN-alpha im), MGb2-PAD-MMC (ip) and MGb2-PAD-MMC+Hu-IFN-alpha daily for 5 d beginning 4 h after inoculation. The efficacy of the reagents estimated by the reduction of tumor size and calculated by T/C (%), was 28.3%, 16.4%, 47.8%, and 83.1%, respectively. These results demonstrated that the antitumor effect of MGb2-PAD-MMC was superior to free MMC, and that the Hu-IFN-alpha might further enhance the action of MGb2-PAD-MMC.

Adenocarcinoma↗

PubMed1993

Limited joint mobility of the hand: prevalence and relation to chronic complications in non-insulin-dependent diabetes mellitus patients.

A total of 170 non-insulin-dependent diabetes mellitus (NIDDM) patients admitted to Kaohsiung Chang Gung Memorial Hospital during the period from January 1988 to December 1989 were examined for the presence of cheiroarthropathy. Fifty-four percent (92 patients) had limited joint mobility (LJM) of the hand, a prevalence significantly higher than that of non-diabetic controls (7%). Duration of diabetes was positively related to the severity of LJM (p = 0.03, chi-square contingency table). Chronic diabetic complications such as cataracts (p = 0.04) and overt proteinuria (p = 0.03) were also associated with the presence of LJM, and diabetic retinopathy (p = 0.007); vision-threatening retinopathy was strongly associated with the presence of LJM (p = 0.0002). The sex ratio, HbA1c and creatinine clearance rates did not show significant differences between patients with and without LJM. In conclusion, the occurrence of LJM of the hand in NIDDM patients observed at this hospital is common and is often accompanied by other chronic diabetic complications. Its presence should alert physicians to other associated diabetic complications with increased morbidity and mortality.

Adult↗

PubMed1993

Extended Kalman filter (EKF) application in vitamin C two-step fermentation process.

Based on kinetic model study of vitamin C two-step fermentation, the extended Kalman filter (EKF) theory is conducted for studying the process which is disturbed by white noise to some extent caused by the model, the fermentation system and operation fluctuation. EKF shows that calculated results from estimated process parameters agree with the experimental results considerably better than model prediction without using estimated parameters. Parameter analysis gives a better understanding of the kinetics and provides a basis for state estimation and state prediction.

Ascorbic Acid↗