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Biomedical subjects

J Chow

Publications and source records attributed to J Chow.

At least 55 records · Page 3Linked to original sources
PubMed1995

Prostatic non-Hodgkin's lymphoma causing acute urinary retention in childhood.

An 8-year-old boy presented with dysuria and acute retention of urine. Rectal examination showed a hard mass arising from the prostate. CT scan of the pelvis confirmed the presence of a large prostatic tumor causing bladder outflow obstruction. A provisional diagnosis of pelvic sarcoma was initially made. Biopsy of the tumor mass however, revealed non-Hodgkin's lymphoma of T-cell type. The tumor showed very good response to chemotherapy and the urinary obstruction significantly improved with a week after starting therapy.

Acute Disease↗
PubMed1995

High-level production from a baculovirus expression system and biochemical characterization of human GMP synthetase.

GMP synthetase, a key enzyme in the de novo synthesis of guanine nucleotides, is a potential target for immunosuppression and anticancer chemotherapy. In order to closely examine the catalytic mechanism and active-site topography of this enzyme, large amounts of pure protein are needed. Catalytically active human GMP synthetase was expressed in a baculovirus system. A high-level production system has been established from which the yield of pure protein is routinely more than 50 mg/10 liters of cell culture. The recombinant enzyme was purified to homogeneity and characterized. Like native GMP synthetase, the recombinant enzyme was resolved into two forms by ion-exchange chromatography. The two forms are both monomers and they differ in their isoelectric points. There is no evidence that these forms are in equilibrium or interconvertible. Protein sequence analysis reveals that both forms are blocked at the amino-terminus and they are essentially identical in sequence. Since they can be produced by a cDNA with a single open reading frame, we believe that they represent post-translational modification variants. The recombinant GMP synthetase is not distinguishable from the native enzyme in terms of chromatographic profiles, subunit composition, molecular weight, and kinetic properties. The inhibition constants and the modes of inhibition toward decoyinine, a selective inhibitor of GMP synthetase, are also the same as the native enzyme. The high-level production of active enzyme is invaluable to the determination of the three-dimensional structure and the discovery of potent and selective drug candidates.

Animals↗
PubMed1995

The stability of segmentalized Le Fort I osteotomies with miniplate fixation in patients with maxillary hypoplasia.

PURPOSE: This study evaluates the postsurgical stability of segmentalized Le Fort I osteotomies with miniplate fixation in patients with maxillary hypoplasia. MATERIALS AND METHODS: Eighteen adult patients who had undergone segmentalized Le Fort I osteotomy for anterior and inferior repositioning of their hypoplastic maxilla were studied radiographically. The positional change of five maxillary landmarks (PNS, ANS, A, U1, and UM) were measured on serial cephalometric radiographs according to a reference frame constructed by using the SN line for superimposition, sella as the origin of the coordinates, and a line parallel to Frankfort horizontal plane as the x-axis. The positional changes of all variables were measured twice, and the means were calculated for analysis. The paired t-test was used for statistical analysis. RESULTS: Statistically significant mean vertical change (P < .01) was found in the anterior maxilla, with U1 having moved up by 27.8% (1.5 mm) of its initial downward surgical movement by 1 year postoperatively. U1 and UM had moved forward 2.0 mm and 1.5 mm, respectively (P < .01) by 1 year postoperatively, but the bony landmarks had no statistically significant change in their horizontal positions. CONCLUSION: Although statistically significant postsurgical changes were found at 1 year postoperatively, overcorrection is not recommended because of the large individual variation observed and the relatively small magnitude of the relapse.

Adult↗
PubMed1995

Community level factors and child maltreatment rates.

Using census and administrative agency data for 177 urban census tracts, variation in rates of officially reported child maltreatment is found to be related to structural determinants of community social organization: economic and family resources, residential instability, household and age structure, and geographic proximity of neighborhoods to concentrated poverty. Furthermore, child maltreatment rates are found to be intercorrelated with other indicators of the breakdown of community social control and organization. These other indicators are similarly affected by the structural dimensions of neighborhood context. Children who live in neighborhoods that are characterized by poverty, excessive numbers of children per adult resident, populations turnover, and the concentration of female-headed families are at highest risk of maltreatment. This analysis suggests that child maltreatment is but one manifestation of community social organization and that its occurrence is related to some of the same underlying macro-social conditions that foster other urban problems.

Adolescent↗
PubMed1994

Purification, characterization and selective inhibition of human prostaglandin G/H synthase 1 and 2 expressed in the baculovirus system.

Human prostaglandin G/H synthase 1 and 2 were expressed in the baculovirus expression system and purified to high levels. Both enzymes were glycosylated. PGHS-1 appeared to be homogeneous by SDS-PAGE analysis but two closely migrating bands were detected in PGHS-2 preparation which were evidently due to heterogeneity in glycosylation. The amino-acid sequence of the N-termini of both isoforms indicated that the signal sequences were efficiently cleaved by the insect cells. The recombinant human PGHS-1 and PGHS-2 possessed both cyclooxygenase and peroxidase activities. Both had high affinities for arachidonate as substrate and underwent self-inactivation during catalysis. The recombinant isoforms were not pharmacologically identical, since some NSAIDs were selective inhibitors of either PGHS-1 or PGHS-2. This is the first report of high levels of expression and purification of human PGHS isoforms. The recombinant enzymes are invaluable in developing potent PGHS-2 selective inhibitors that may be efficacious anti-inflammatory drugs with no or low levels of toxicity.

Amino Acid Sequence↗
PubMed1994

Production, purification, and characterization of human matrilysin (PUMP) from recombinant Chinese hamster ovary cells.

A process for semicontinuous production of matrilysin zymogen secreted from recombinant Chinese hamster ovary (CHO) cells was developed. The zymogen was purified to apparent homogeneity by sequential ion-exchange and metal chelation chromatography. These processes were scaled-up to purify gram quantities of the zymogen. The N-terminus of the secreted zymogen from the recombinant cells was the same as the observed sequence of the zymogen from natural sources. Furthermore, activation and autocatalysis of the recombinant zymogen resulted in a form with an N-terminus identical to that of the corresponding native enzyme. The three C-terminal amino acids of both the recombinant zymogen and the corresponding smaller activated form were missing. Activated matrilysin was shown to have activity against a synthetic peptide substrate. The large quantities of matrilysin that can be produced and purified from the recombinant CHO cells will be useful in determination of the structure of matrilysin.

Amino Acid Sequence↗
PubMed1994

Epstein-Barr virus-associated gastric lymphoma in Hong Kong Chinese.

We report 11 cases of gastric lymphoma that harbor the Epstein-Barr virus (EBV) encoded small messenger RNA, EBER-1, detected by in situ hybridization. The cases represented 18% of 61 consecutive gastric lymphomas from three institutions in Hong Kong between 1988 and 1993. The mean age of patients was 62 years (range, 33 to 87). The male to female ratio was 5:6. Nine of the 11 (81.8%) EBER-1+ gastric lymphomas were diffuse large cell lymphomas of B-cell type without low grade components. Macroscopically these lymphomas appeared either as large noncleaved cell (centroblastic) or immunoblastic type. From the available follow-up data, five of the nine patients with B-cell lymphoma were alive and well 48, 40, 14, 13, and 12 months, respectively, after gastrectomy and chemotherapy. One patient died of postoperative pneumonia and one died of a second malignancy (esophageal squamous carcinoma) 40 months after gastrectomy. None of the EBER-1+ B-cell gastric lymphomas showed histological features characteristic of low grade lymphoma of the mucosa-associated lymphoid tissue (MALT) type reported to be common in some Western countries. Of the two patients with T-cell lymphoma, one had a pleomorphic T-cell lymphoma and the other had an angiocentric lymphoma. The former was lost to follow-up after the biopsy and the latter presented with gastric perforation and died 1.5 months after gastrectomy. It is concluded that a significant proportion of gastric lymphomas in Hong Kong Chinese are EBV-related and that they show histological features more akin to conventional node-based lymphomas than to MALT-type lymphomas.

Adult↗
PubMed1994

Ultrasound findings in renal parenchymal disease: comparison with histological appearances.

Ultrasound examination was carried out in 55 patients undergoing renal biopsy for suspected renal parenchymal disease. Analysis of sonographic and histological findings showed statistically significant positive correlations between renal size and the extent of glomerular hyper-cellularity and crescent formation and between cortical echogenicity and severity of glomerular sclerosis, crescent formation, interstitial inflammatory cell infiltration, tubular atrophy and interstitial fibrosis. Positive correlation was also observed between prominence of the medullary pyramids and glomerular sclerosis. The most marked sonographic abnormalities were seen in proliferative (including crescentic) glomerulonephritis, diabetic glomerulosclerosis and tubulo-interstitial nephritis. IgA, membranous and minimal change nephropathy were less likely to be associated with sonographic abnormalities. We conclude that certain sonographic appearances in renal parenchymal disease reflect the presence and severity of light microscopical abnormalities but, although ultrasound assessment provides a high positive predictive value for renal parenchymal disease, specific conditions cannot be distinguished.

Adult↗
PubMed1994

Coccoid forms of Helicobacter pylori in the human stomach.

Helicobacter pylori (HP) may transform from helical bacillary forms to coccoid forms after several days' in vitro incubation. The authors examined 111 consecutive gastrectomy specimens for the presence of coccoid forms of H pylori. Tissues from 64 stomachs (57.7%) showed colonization by H pylori, including 49 cases (76.6%) of adenocarcinoma, 14 cases (21.9%) of benign peptic ulcer, and 1 case (1.6%) of malignant lymphoma. Of these, coccoid forms of H pylori were identified in 53 cases (82.8%). In hematoxylin-and-eosin-stained sections coccoid forms of H pylori appeared as solid, round, basophilic dotlike structures. Under an electron microscope, coccoid forms of H pylori appeared as U-shaped bacilli, with the ends of the two arms joined by a membranous structure. Ultrastructural findings were identical to those from cultures of H pylori. With anti-Helicobacter antibody, coccoid forms of H pylori were positively stained by immunoperoxidase. Helical bacillary forms of H pylori invariably coexisted with the coccoid forms. By semiquantitative analysis, the number of coccoid forms in adenocarcinoma was significantly (P > .01) greater than that in benign peptic ulcers. This study confirms that H pylori can exist in coccoid forms in the human stomach. Coccoid forms should be distinguished from the pathogenic or nonpathogenic bacterial cocci, fungal spores, and cryptosporidia that may colonize the human stomach.

Adenocarcinoma↗
PubMed1994

Coupling between mRNA synthesis and mRNA stability in Escherichia coli.

Transiently stable products derived from the endonuclease cleavage of transcripts from the secEnusG and rplKAJLrpoBC operons have been identified. Cleavage sites for RNase III occur in the leader of the secEnusG transcript and in the L12-beta intercistronic space of the rplKAJLrpoBC transcript. A single RNase E cleavage site was located in the L1-L10 intergenic space. Inactivation of RNase III and RNase E results respectively in a one- to twofold and a greater than 10-fold stabilization of five mRNA sequences from within the secE, nusG, L11-L1, L10 and beta encoding cistrons. The relative amounts of each of these five mRNA sequences were found to be nearly constant when measured either in the presence or absence of cleavage by RNase III or RNase E. This clearly implies that any increases in the stability of these mRNA sequences resulting from the inactivation of processing by RNase III or RNAase E are counterbalanced by changes in the mRNA synthesis rates. The mechanism that links mRNA synthesis to mRNA decay is not known.

Bacterial Proteins↗
PubMed1994

Ondansetron for prevention of postoperative nausea and vomiting following minor oral surgery: a double-blind randomized study.

The efficacy and safety of ondansetron in preventing postoperative nausea and vomiting following minor oral surgery was evaluated in a prospective randomized double-blind study. Of a total of seventy-seven patients, randomly 38 had 4 mg of ondansetron and 39 had normal saline as placebo intravenously immediately prior to induction of anaesthesia. A standard general anaesthetic with thiopentone, suxamethonium, fentanyl, nitrous oxide and isoflurane was employed. Postoperatively nausea was assessed verbally and on a visual analog scale at 1, 4 and 24 hours from the time of awakening. Episodes of vomiting were recorded. Eight patients (21.1%) in the ondansetron group compared to 19 (48.7%) in the placebo group had nausea (P < 0.05) and 1 (2.6%) in the ondansetron group compared with 9 (23.1%) in the placebo group vomited (P < 0.05). Patients who vomited twice or more and the number who required a rescue antiemetic were significantly fewer in the ondansetron group (P < 0.05). Cardiovascular parameters were stable and showed no significant difference in the two groups. There were no significant adverse effects that could be directly attributable to ondansetron.

Adolescent↗
PubMed1993

Overexpression, purification and characterization of human recombinant 15-lipoxygenase.

Human 15-lipoxygenase was expressed to high levels (approx. 20% of cellular protein) in a baculovirus/insect cell expression system. Catalytically active enzyme was readily purified (90-95% pure) from cytosolic fractions by anion-exchange chromatography on a Mono Q column with approx. 95% recovery of enzymatic activity. Routinely, a yield of 25-50 mg of pure enzyme per L of culture and a specific activity of 7.1-21 mumol 13-hydroxyoctadecadienoic acid (13-HODE)/mg.min (turnover rate of 8.4-25 s-1) were obtained. Both the specific activity and the enzyme's iron content was significantly increased by the addition of ferrous ions to either the purified enzyme or to the insect cell culture medium during production. An isoelectric point of 5.85 was determined and the N-terminal amino acid sequence was found to be identical to that predicted from the cDNA. The purified recombinant enzyme exhibits a dual positional specificity with arachidonic acid (formation of 15S- and 12S-hydroxyeicosatetraenoic acid (12S-HETE) in a ratio of 12:1). Double oxygenation products 14R,15S- and various 8,15-DiHETE isomers were also identified. With linoleic acid as substrate, a pH-optimum of 7.0 and a KM of 3 microM were determined. The enzyme undergoes suicidal inactivation during fatty acid oxygenation, is sensitive to standard lipoxygenase inhibitors, and oxygenates phospholipids, cholesterol esters, biomembranes and human low-density lipoprotein. Contrary to prior studies on the rabbit enzyme, no glycosylation was detected.

Animals↗
PubMed1992

An assessment of the prevalence of organic material on bone surfaces.

Although an unmineralized layer of organic material has been identified on both bone-forming surfaces and surfaces upon which bone formation has ceased (quiescent surfaces), the proportion of bone surfaces that is covered by unmineralized material has not been quantified. Because the unmineralized layer may play a role in the regulation of bone resorption, we undertook a scanning electron microscopy (SEM) assessment to determine its extent. Specimens of adult human ribs were prepared for undecalcified resin sections and SEM. For SEM, cells were removed and the bone surface was inspected and photographed. The same specimen was then immersed in NaOCl to remove organic material, and inspected again in the SEM. We found that the surface of bone appeared quite different before, compared to after, removal of organic material. Before removal, the entire nonresorptive surface was finely fibrillary. After removal of the organic material we observed a minor component showing the finely nodular surface typical of mineralizing bone, and a major component in which the mineral surface was free of such nodules. In only 3 of 1,200 photographs did we identify areas in which the bone surface was not altered by removal of organic material from the specimen. Analysis of histological sections of the ribs showed that approximately 85% of the bone surface was classifiable by light microscopy as quiescent. These results suggest that not only formative but also quiescent surfaces are covered by a layer of unmineralized organic material.

Adult↗
PubMed1992

ICAM-1 expression in renal disease.

AIM: To determine the role of intercellular adhesion molecule-1 (ICAM-1) in immune mediated damage in glomerulonephritis, and whether its expression correlates with disease activity. METHODS: Fifty three renal biopsy specimens from a range of non-immune renal disease and low grade and high grade glomerulonephritides were stained with ICAM-1. Positivity was assessed in the tubules. Tubular damage and accompanying interstitial inflammation were also noted. The ICAM-1 positivity in damaged and undamaged tubules was correlated with the three groups of renal disease. RESULTS: ICAM-1 positivity in undamaged tubules was observed in glomerulonephritis, and this showed a strong correlation with disease activity. In contrast, ICAM-1 positivity on damaged tubules correlated with evidence of chronic tubular damage, and was seen in a large proportion of cases, regardless of the underlying disease. There was no correlation between ICAM-1 positivity and a local lymphocytic infiltrate. CONCLUSION: ICAM-1 probably has an important role in the pathogenesis of glomerulonephritis. Its expression may be secondary to cytokines released by cells participating in the glomerular damage. As these cytokines also influence tubule function, tubular ICAM-1 expression may be a marker of the extent of tubular disturbance in glomerulonephritis.

Cell Adhesion Molecules↗
PubMed1992

Estrogen maintains trabecular bone volume in rats not only by suppression of bone resorption but also by stimulation of bone formation.

Estrogen is generally considered to maintain bone mass through suppression of bone resorption. We have previously demonstrated that administration of pharmacologic doses of estrogen increases bone formation in ovary-intact rats. To assess the effects of physiological concentrations of estrogen on bone formation, estrogen was administered to ovariectomized rats in which bone resorption was suppressed by the bisphosphonate 3-amino-1-hydroxypropylidene-1-bisphosphonate (AHPrBP). Animals receiving exogenous 17 beta-estradiol (E2) (1, 10, and 100 micrograms/kg daily for 17 d) showed a dose-dependent increase in trabecular bone volume of 1.9, 25.8, and 43.6%, respectively, compared with those rats treated with AHPrBP alone. The increase in bone volume was associated with an increase in bone formation in E2-treated animals, in which bone resorption had been almost completely suppressed by AHPrBP. Neither ovariectomy, AHPrBP, nor E2 treatment had a significant effect on the volume or rate of formation of cortical bone. Thus, the increased bone resorption, which is a consequence of estrogen-deficiency, entrains increased bone formation, which masks a simultaneous reduction in estrogen-dependent bone formation. Therefore, in addition to the nonspecific effect of estrogen to depress formation via coupling, we have identified a specific effect of estrogen to increase formation independent of coupling. Thus it appears that estrogen maintains bone volume not only through inhibition of bone resorption, but also through stimulation of bone formation.

Animals↗
PubMed1991

Physicochemical characterization of recombinant human nerve growth factor produced in insect cells with a baculovirus vector.

Recombinant human nerve growth factor (rhNGF) secreted by insect cells was purified by ion-exchange and reversed-phase chromatography to near homogeneity. The N-terminus of the secreted molecule was analogous to that of mouse salivary gland NGF. In its native conformation, the insect cell produced rhNGF molecules were homodimers consisting of 120 amino acid polypeptide chains. Mature rhNGF was found not to be significantly glycosylated (less than 0.08 mol of N-acetylglucosamine/mol of protein). The rhNGF was homogeneous with regard to molecular weight and amino acid sequence. Isoelectric focusing resolved the rhNGF into one major and one minor component. Because rhNGF from insect cells can be obtained in large quantities, purified to near homogeneity, and is similar to natural NGF with regard to physicochemical properties and biological activity, it is suitable for further evaluation in animal models as a therapeutic molecule for neurodegenerative diseases such as Alzheimer's disease.

Amino Acid Sequence↗