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Biomedical subjects

L Tan

Publications and source records attributed to L Tan.

At least 181 records · Page 10Linked to original sources
PubMed1987

The aromatase active site: the C-6 "front" side of the androgen molecule is required for binding.

Solubilized microsomes from human placenta were partially purified by anion-exchange chromatography on a quaternary methylamino-silica column. The aromatase-active fractions were then used for measuring optical difference spectra with various androgens, substituted at positions C-1, 2, 6, 11, 16, 17, and 19. Of these, only androgens substituted at the C-6, or frontside of the steroid backbone induce a strong type I spectrum, as well as competitive inhibition with the natural substrate, 4-androstene-3,17-dione. An in-house made affinity support, synthesized by reacting 6 beta-bromo-androstenedione with aminohexyl-Sepharose at pH 10-11 via a SN2-mechanism, was unable to trap the aromatase cytochrome P-450 component of the enzyme. A 3-dimensional model of the active site accounting for these interactions is proposed.

Androgens↗
PubMed1987

Inhibition of cytochrome P-450-linked monooxygenase systems by naphthoquinones.

Several naphthoquinones, except 2-hydroxy-1,4-naphthoquinone, were found to inhibit microsomal cytochrome P-450-linked monooxygenase activities in rabbit liver and human placenta. In particular, 5-hydroxy-1,4-naphthoquinone inhibited placental estrogen biosynthesis more effectively than it did hepatic drug oxidation reactions. There was little contribution by superoxide radicals to these enzyme inhibitions by naphthoquinones. Spectrophotometric studies revealed that naphthoquinones bind to the cytochrome P-450 component of the monooxygenase complex in both microsomal systems, suggesting that the inhibition is caused by direct interaction of these compounds with the heme.

Androstenedione↗
PubMed1987

Computed tomography and ultrasound diagnosis of mycotic aneurysm of the abdominal aorta due to Salmonella.

The case of a 56 year old diabetic Chinese male, with a Salmonella bovismorbificans (serogroup C) mycotic aneurysm of the abdominal aorta is presented. The lesion was seen by computed tomography and ultrasound and the patient was successfully treated by primary resection, debridement and grafting. Computed tomography criteria for the diagnosis of mycotic aneurysms of the abdominal aorta are discussed. Ultrasound identified the aortic aneurysm correctly but was unable to demonstrate the associated psoas abscess in this case.

Aneurysm, Infected↗
PubMed1987

Behavior of dentists and child patients during treatment.

This study is part of a larger research project which aims to analyze children's dental fear by making a detailed analysis of the behavioral interactions between dentists and anxious child patients. The behavior of 12 high- and 12 low-anxious children was recorded on videotape during two dental visits in which the children were treated by either experienced or inexperienced dentists. Results indicated a relation between the dentist's experience in treating anxious children and the behavior of child patients. In general, children treated by experienced dentists showed more fear-related behaviors. Furthermore, the behavior of the dentist was related to both his experience and the fear level of the child patient. Experienced dentists showed more communicative behaviors than the inexperienced dentists, but all dentists communicated more with high- than with low-anxious children. Experienced dentists worked faster than inexperienced dentists, but treatment of the high-anxious children was not more time-consuming than treatment of the low-anxious children.

Anxiety↗
PubMed1987

Genetically engineered antibody molecules and their application.

Immunoglobulin genes can be efficiently expressed following transfection into myeloma cells. Using protoplast fusion, transfection frequencies greater than 10(-3) can be achieved. Compatible plasmids containing two different selectible markers are used to simultaneously deliver heavy and light chain genes to the same cell. To produce molecules with differing specificities the rearranged and expressed variable regions can be cloned from the appropriate hybridoma. In some cases, variable regions from cDNAs can be inserted into the expression vectors. It is possible to manipulate the immunoglobulin genes and produce novel antibody molecules. Antibodies have been produced in which the variable regions from mouse antibodies have been joined to human constant regions. In addition, antibodies with altered constant regions have been produced. These genetically engineered antibodies provide a unique set of reagents to study structure-function relationships within the molecule. They also can potentially be used in the diagnosis and therapy of human disease.

Animals↗
PubMed1987

U wave inversion in unstable angina due to left main coronary artery stenosis.

A 50-year-old male was admitted to hospital for repeated episodes of chest pain due to unstable angina. Serial electrocardiograms were all normal except for one electrocardiogram, recorded during chest pain, which showed isolated U wave inversion in leads I, V4 and V5. Subsequently, selective coronary arteriography showed isolated 99% stenosis of his left main coronary artery.

Angina Pectoris↗
PubMed1986

Normal-phase high-performance liquid chromatographic separations of positional isomers of substituted benzoic acids with amine and beta-cyclodextrin bonded-phase columns.

The separation of positional isomers of several substituted benzoic acids was studied using two different columns, i.e. amine and beta-cyclodextrin bonded silicas, at appropriate normal-phase conditions. Although some other columns do separate substituted benzoic acids, particularly the octadecylsilica column in a reversed-phase mode, the present separation under simple normal-phase, isocratic conditions is unique. In particular, the retention order of these acids for the amino bonded-phase column can be roughly predicted using the pKa values of the analytes. On the other hand, due to the strong interaction between substituted benzoic acids and the beta-cyclodextrin bonded phase, a small amount of acetic acid has to be added into the mobile phase to overcome band broadening and tailing problems. Possible retention mechanisms are also discussed.

Amines↗
PubMed1986

Stereochemistry of estrogen biosynthesis by a reconstituted aromatase cytochrome P-450 preparation from human placenta.

According to the literature, the multistep reaction mechanism of estrogen biosynthesis proceeds with stereospecific loss of the equatorial 1 beta-, and axial 2 beta-protons. These results were deduced from experiments carried out, either with crude microsomes, or at best with impure enzyme extracts. However, when [1,2- 3H]4-androstene-3,17-dione of known absolute 3H-label distribution was incubated with a reconstituted enzyme system, consisting of homogeneous NADPH-cytochrome P-450 reductase and highly purified aromatase, we obtained results that can only be logically explained by a trans- and antiparallel elimination reaction of both the axially oriented C-2 beta-, and C-1-alpha protons. We further demonstrate that the reconstituted enzyme has an aromatase activity optimum at pH 7.2, and an apparent Km of 0.66 microM for NADPH and of 0.24 microM for 4-androstene-3,17-dione. Also, the enzyme requires 3 nmoles of NADPH for each nmole of estrogen that is formed.

Androstenedione↗
PubMed1986

Purification and reconstitution properties of human placental aromatase. A cytochrome P-450-type monooxygenase.

The hemoprotein component of human placental aromatase (estrogen synthetase) has been purified to a high degree of homogeneity by a combination of affinity and adsorption chromatography on aminohexyl-Sepharose, concanavalin-A-Sepharose, and hydroxyapatite. The monomeric form of the enzyme has an Mr of 55000 +/- 1000 as estimated by sodium dodecyl sulfate gel electrophoresis. Its absolute spectrum shows a high-spin Soret band at 394 nm while its reduced, CO-difference spectrum has a maximum at 447 +/- 1 nm. Full reconstitution of aromatase activity was obtained when it was recombined with a homogeneous preparation of the higher-Mr form of either human placental, or bovine hepatic NADPH-cytochrome P-450 reductase. Critical factors for purification of the very unstable, membrane-bound hemoprotein with good retention of activity were, besides the chromatographic sequence, the use of the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (Chaps) during the solubilization, and the stabilizing effect of the aromatase substrate, 4-androstene-3,17-dione, throughout the procedure. In the presence of NADPH, the reconstituted enzyme system smoothly aromatizes 19-oxoandrostenedione, 19-hydroxyandrostenedione and androstenedione in this order of reactivity. The same reconstituted system also aromatized testosterone, but it was inactive towards 19-norandrostenedione. Known cytochrome P-450 inhibitors decreased its activity. We conclude: (a) the terminal oxidase of human placental aromatase is indeed a cytochrome P-450-type monooxygenase; (b) the multistep aromatization reaction of C19 androstenes is catalyzed by a single enzyme; (c) aromatization of 19-norsteroids reported by other authors must be due to a different aromatase. Experimental data obtained with the reconstituted enzyme are fully compatible with the concept of a reaction mechanism for the aromatization sequence involving an all-trans, antiparallel elimination of the 19-methyl group, the 2 beta proton and the 1 alpha proton, rather than the 1 beta proton, as generally assumed.

Adult↗
PubMed1986

In vitro susceptibility of the Bacteroides fragilis group in community hospitals.

The antimicrobial susceptibility of clinical isolates of the Bacteroides fragilis group was determined at six community hospitals (one large, greater than 600 beds; and five smaller, 96-325 beds). Imipenem was the most active beta-lactam with 100% of isolates being sensitive at 4 micrograms/ml. The percentage of isolates inhibited at 16 micrograms/ml (and 32 micrograms/ml) for the 7-alpha-methoxy antibiotics was: cefoxitin 66 (90); moxalactam 73 (85); cefotetan 68 (72); cefmetazole 40 (61). Metronidazole, chloramphenicol, and clindamycin were active against 100%, 100%, and 89% at breakpoints of 8 micrograms/ml, 8 micrograms/ml, and 4 micrograms/ml, respectively. The activity of several beta-lactams in our report differed slightly from that reported from university teaching hospitals. There were differences at many of the breakpoints for activity of some of the beta-lactam antibiotics for isolates from the large community hospital as compared with the combined isolates from the smaller community hospitals. Interestingly, the pattern was one of more resistance at the smaller community hospitals.

Anti-Bacterial Agents↗
PubMed1986

Physiologic changes induced by endotracheal instillation and suctioning in critically ill preterm infants with and without sedation.

Endotracheal instillation and subsequent suctioning produces fluctuations of intracranial pressure (ICP), mean arterial pressure (MAP), and cerebral perfusion pressure (CPP) in sick preterm infants. In an attempt to observe if these fluctuations could be minimized using sedation, we studied a group of seven sick mechanically ventilated preterm infants with and without sedation. Continuous monitoring of ICP, MAP, heart rate, CPP, and arterial oxygen tension (PaO2) were obtained. The statistical analysis of the data revealed significant blunting of fluctuations of MAP, ICP, and CPP with sedation.

Blood Pressure↗
PubMed1986

Purification and properties of human placental NADPH-cytochrome P-450 reductase.

Human placental NADPH-cytochrome P-450 reductase (EC 1.6.2.4) was purified to electrophoretic homogeneity in two chromatographic steps with a high retention of bioactivity. After solubilization with 1% sodium cholate in a protective medium containing 20% glycerol, 10 microM 4-androstene-3,17-dione, 1 mM dithiothreitol, and 0.2 mM EDTA, a 35-60% ammonium sulfate precipitate was prepared. The crude protein mixture was then applied to a 2',5'-ADP-Sepharose 4B affinity column, followed by high-performance anion-exchange chromatography (Pharmacia Mono-Q column). Two forms of the reductase were isolated. One was eluted at higher salt concentration and had a relative mass (Mr) of 79 kdaltons (kDa) as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance gel permeation chromatography. A smaller size reductase with a Mr of 70 kDa, eluting at lower salt concentration, was also formed by trypsinolysis of the 79-kDa reductase. It must therefore be regarded as a proteolytic artifact. The absolute spectra in the visible region of the two reductases were identical with maxima at 376 and 452 nm, typical of a flavoprotein. They also had the same specific activity of 24.7 +/- 0.7 mumol/min per milligram protein towards cytochrome c. However, only the 79-kDa reductase showed aromatase-reconstitution activity. The homogeneity of these reductases was further confirmed by the appearance of a single peak when subjected to gradient, reversed-phase high-performance liquid chromatography. According to its amino acid composition, the 79-kDa reductase is a highly acidic and hydrophobic protein, composed of 695 residues.

Amino Acids↗
PubMed1986

Treatment of irresectible hepatocellular carcinoma with intrahepatic arterial lipoidal mixed with adriamycin and mitomycin C.

Four patients with advanced hepatocellular carcinoma, but with stage I functional disease, were treated with intrahepatic arterial lipoidal mixed with small doses of Adriamycin (20 mg) and Mitomycin C (10 mg). Regression was seen in 3 out of the 4 patients. In 2 patients, there was substantial regression of tumour clinically, radiologically and biochemically. The treatment was tolerable without marrow depression or deterioration of liver function. Mild fever (37 degrees C) was seen in 2 and epigastric pain in 1. This form of treatment opens up scope for further improvement in the management of irresectable hepatocellular carcinoma.

Adult↗
PubMed1986

Ultrasonography in the diagnosis of cholestatic jaundice.

Fifty consecutive patients (32 males and 18 females) with cholestatic jaundice were examined by grey-scale ultrasound from June 1981 to June 1983. All patients were studied without access to case notes. All patients had a diagnosis established by subsequent liver biopsy, clinical course, surgery or autopsy. Using the presence or absence of a dilated biliary system as the criterion, intrahepatic or extrahepatic cholestasis was correctly differentiated in 48 of the 50 patients, giving an overall accuracy of 96%. All 16 patients with intrahepatic cholestasis were correctly identified. Two of the 34 patients with extrahepatic cholestasis, each of whom had biliary stones, were misdiagnosed as intrahepatic cholestasis. In the 34 patients with extra-hepatic cholestasis, site of obstruction was defined in 55.9%, and specific aetiology diagnosed in 44.1%. Ultrasound proves to be an accurate method for the evaluation of cholestatic jaundice, and would have a definite value as a screening test before proceeding to invasive studies.

Cholestasis, Extrahepatic↗