Search PubMed⌕ Search

Biomedical subjects

B Christensen

Publications and source records attributed to B Christensen.

At least 109 records · Page 6Linked to original sources
PubMed1994

Preoperative methionine loading enhances restoration of the cobalamin-dependent enzyme methionine synthase after nitrous oxide anesthesia.

BACKGROUND: Prolonged exposure to nitrous oxide causes adverse effects mimicking those of cobalamin deficiency. This is explained by irreversible oxidation of cobalamin bound to the enzyme methionine synthase. The inactivation of methionine synthase by nitrous oxide in cultured human fibroblasts is decreased at high concentrations of methionine in culture medium. METHODS: We investigated the possible protection against cobalamin inactivation by preoperative methionine loading in patients undergoing nitrous oxide anesthesia. Fourteen patients receiving anesthesia for 75-230 min were included. Half of these patients received a peroral methionine loading dose 2 h before anesthesia. RESULTS: After nitrous oxide exposure, a considerable inactivation of methionine synthase in mononuclear white blood cells was seen in all patients, reaching a nadir after 5-48 h. In the patients not subjected to a methionine load, recovery of enzyme activity was not complete within 7 days. In the patients receiving a methionine load, the kinetics of inactivation of methionine synthase were similar, but the rate and extent of enzyme recovery was higher than in patients not receiving methionine, and in four patients, the enzyme activity even exceeded the preoperative level. The inactivation of methionine synthase was associated with a transient increase in plasma homocysteine, and the homocysteine concentration was still increased (mean 28.7%) 7 days after anesthesia in the patients not receiving methionine. A marked peak in homocysteine concentration was observed immediately after anesthesia in the methionine-loaded patients, but the homocysteine level was still increased (mean of 30.5%) after 7 days. The activity of the other cobalamin-dependent enzyme, methylmalonyl coenzyme A mutase, in the mononuclear white blood cells, and the serum concentration of the cobalamin marker methylmalonic acid, were not altered after nitrous oxide anesthesia or methionine loading or both. CONCLUSIONS: Our data suggest that short time exposure to nitrous oxide selectively impairs the function of the cobalamin-dependent methionine synthase. Furthermore, preoperative administration of methionine should be considered as a means to counteract adverse effects of nitrous oxide.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1994

Effect of methionine and nitrous oxide on homocysteine export and remethylation in fibroblasts from cystathionine synthase-deficient, cb1G, and cb1E patients.

We investigated the nitrous oxide-induced inactivation of methionine synthase and the concurrent homocysteine (Hcy) export in mutant fibroblasts with defects in the homocysteine catabolizing enzyme, cystathionine beta-synthase, or in methionine synthase, which carries out homocysteine remethylation. The fibroblasts were incubated in various concentrations of methionine to create conditions favoring methionine conservation or catabolism. In cystathionine beta-synthase-deficient cells, high medium methionine partly protected the enzyme against inactivation, as previously found in normal fibroblasts. The Hcy export rate at low methionine levels was low (0.2-0.6 nmol/h/10(6) cells), and increased 2-3-fold at high methionine levels. Nitrous oxide enhanced Hcy export rate at low methionine, so that in the presence of nitrous oxide, the Hcy export became less dependent of methionine. In cb1G cells, the enzyme inactivation was moderate and independent of medium methionine. The Hcy export rate was intermediate (0.5-0.8 nmol/h/10(6) cells) at low methionine levels, and increased moderately (< 2-fold) at high methionine levels or following nitrous oxide exposure. In cb1E mutants, the enzyme activity was not affected by nitrous oxide, and the Hcy export was high (0.8-1.6 nmol/h/10(6) cells) and independent of methionine and nitrous oxide. These data suggest that Hcy remethylation and cystathionine beta-synthase activity are major determinants of Hcy export at low and high methionine, respectively. The low susceptibility of methionine synthase to nitrous oxide in the presence of high methionine or in cb1G or cb1E mutants is probably related to low catalytic turnover.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1993

[Early amniocentesis].

Genetic amniocentesis performed at 7-14 weeks of gestation was studied in a series of 138 patients of whom 50 wanted termination of pregnancy (< or = 12 weeks). The material for analysis consisted of 132 samples due to two sampling failures and four samples being handled incorrectly. Forty-eight samples (36 percent) were taken at 7-12 weeks of gestation, mainly transvaginally (36/48:75 percent). The success rate of culture and karyotyping increased with the duration of pregnancy, but was only satisfactory from week 11 onwards. The time until harvest was then 14-15 days. The transvaginal approach is easy to perform and was accepted by the women, but we experienced bacterial or fungal overgrowth in 17 percent of these samples, whereas no infection occurred in the samples taken transabdominally (n = 96). We conclude that genetic amniocentesis is feasible from week 11, but further studies concerning side effects, especially focusing on the procedure-related abortion risk, should be carried out before early amniocentesis is routinely applied.

Adolescent↗
PubMed1993

[General practitioners and smoking. General practitioners' knowledge, attitudes and smoking habits and the relationship between these assessed by a questionnaire study in the county of Aarhus].

The objects of the investigation were to investigate the smoking habits of general practitioners, their assessment of tobacco as a risk factor for ischaemic cardiac disease, attitudes to intervention to stop smoking and to assess whether there was a connection between these. The project was carried out as a questionnaire investigation in the County of Aarhus, where all of the general practitioners received questionnaires. A total of 313 general practitioners replied to the questionnaire which corresponds to 84% participation. 33% of the general practitioners smoked and nine were chain smokers. The majority of the general practitioners accepted that smoking was a risk factor for ischaemic heart disease and were prepared to make great efforts to combat smoking. A connection was present between smoking habits and attitudes: Non-smokers considered that smoking was of great significance as a risk factor for ischaemic heart disease and were prepared to make efforts to alter the smoking habits of their patients. General practitioners doubted the effect of their advice about stopping smoking.

Attitude of Health Personnel↗
PubMed1993

[General practitioners and prevention of ischemic heart disease].

The object of this investigation was to examine general practitioners' attitudes to prophylaxis, assessment of the significance of a series of risk factors for the development of heart disease and how much emphasis they employed in attempting to alter the risk factors. In addition, the general practitioners' own health habits were investigated and it was assessed whether there was any connection between health habits and assessment of risk factors and the priorities given to these efforts. The general practitioners' advice and current behaviour as regards risk factors were investigated. The investigation was carried out as a questionnaire investigation in the County of Aarhus where all doctors received a questionnaire. A total of 313 general practitioners replied to the questionnaire which corresponds to a percentage participation of 84. The investigation revealed that general practitioners are interested in prophylaxis but find it difficult. By and large, general practitioners regarded the usual risk factors as being of great significance for the development of ischaemic heart disease and considered that it was important to alter these. A connection was present between their own health habits, assessment of risk factors and the priority awarded to these. Practitioners who had had their own serum cholesterol measured, considered that hypercholesterolaemia was important and awarded efforts to correct this greater priority than practitioners who had not had their serum cholesterol measured. The general practitioners abilities in taking case histories and giving dietary advice in cases of hypercholesterolaemia showed that they had only few deficiencies, but that there was a great scatter in their intervention limits for hypercholesterolaemia.

Denmark↗
PubMed1993

Two phorbol ester receptor affinities in partially transformed human urothelial cells and decrease of receptor binding in desensitized cells.

The presence of specific binding sites for phorbol esters was studied in a transformed but non-tumorigenic human urothelial cell line HCV-29 by assay of specific binding of 3H-phorbol-12,13-dibutyrate (3H-PDBu) to intact living cells. 3H-PDBu bound specifically to HCV-29 cells in a saturable and competitive manner. Scatchard plot analysis of specific binding yielded a curved plot consistent with two binding sites with Kd of 11 nM and 102 nM, respectively. At saturation the corresponding PDBu binding capacities (Bmax) were 8.8 pmol/10(6) cells (5.2 x 10(6) molecules bound per cell) and 2.8 pmol/10(6) cells (1.7 x 10(6) molecules bound per cell). 3H-PDBu binding was displaced by biologically active phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and mezerein, but not by tumor promoters such as L-tryptophan, anthranilic acid and sodium saccharin. In cells desensitized by pretreatment with 1 microgram/ml (2 microM) TPA or PDBu for 24 h the level of binding was reduced to 28% of the level in non-exposed cells. The ability of desensitized cells to bind 3H-PDBu was gradually restored within 5-6 days. At the same time the cells became sensitive to the morphological alteration induced by PDBu. This suggests that desensitization of HCV-29 cells is due to a decreased receptor-ligand binding capacity probably associated with down regulation of the phorbol ester receptors.

Caenorhabditis elegans Proteins↗
PubMed1993

Prenatal diagnosis by in situ hybridization on uncultured amniocytes: reduced sensitivity and potential risk of misdiagnosis in blood-stained samples.

Maternal cell contamination was assessed in 18 macroscopically blood-stained amniotic fluid samples from male fetuses. The samples were analysed by double-target fluorescent in situ hybridization (ISH) with Y and X chromosome-specific probes. The only sample with an aberrant karyotype (47,XY, + 18) was also analysed by hybridization with a chromosome 18-specific probe. An interpretation of extensive maternal cell contamination was made in two samples, one of which was the sample with trisomy 18. ISH with the chromosome 18-specific probe on this latter sample showed that the sensitivity of the ISH method for chromosome enumeration of uncultured amniotic fluid samples may be reduced in blood-stained samples. It was calculated that by using ISH for chromosome enumeration of the two extensively contaminated samples, a case of trisomy 21 might have been overlooked in both samples, while a case of trisomy 18 might only have been overlooked in one of the samples. It is concluded that ISH should not be used for chromosome enumeration of uncultured amniotic fluid samples that are macroscopically blood-stained without further technical developments.

Amniotic Fluid↗
PubMed1993

Rapid detection of numerical aberrations of chromosomes 13, 18 and 21 in chorionic mesenchymal cells.

We have devised and evaluated a rapid screening method for the detection of numerical aberrations of chromosomes 13, 18 and 21 in chorionic villus cells. We used non-radioactive in situ hybridization (ISH) with three chromosome-specific probes on overnight-attached mesenchymal cells from chorionic villi. A blind study was performed of 47 karyotypically normal samples, one triploid sample, two samples trisomic for chromosome 21, and two samples from a fetus with putative mosaicism (46/47, +21). All samples were hybridized with the chromosome 18- and 21-specific probes. Thirty samples were additionally hybridized with the chromosome 13-specific probe. The test could be completed within 3-4 days of sampling. In samples disomic with respect to the probed chromosomes, an average of 2 per cent (range 0-9 per cent) had three hybridization signals. By contrast, in the samples trisomic for the probed chromosome(s), 57 per cent (chromosome 13), 51 per cent (chromosome 18), and an average of 74 per cent (55-86 per cent) (chromosome 21) of the nuclei exhibited three signals. In the putative mosaic samples, the number of nuclei with three chromosome 21-specific signals ranged from 41 to 69 per cent. We conclude that this technique rapidly and clearly distinguishes between normal and trisomic/triploid samples, and consequently may be of use in future prenatal diagnosis.

Chorionic Villi↗
PubMed1993

Identity of tumorigenic human urothelial cell lines and 'spontaneously' transformed sublines.

Restriction fragment length polymorphism (RFLP) analysis, comparative marker chromosome analysis, and polymorphic enzyme analysis was carried out on a total of eight human urothelial cell lines and sublines selected according to our knowledge of their HLA-A,B phenotype. RFLP analysis and cytogenetic analysis showed that the cell lines Hu1703He, Hu1922, and T24 are genuine cell lines of different origin. The identity of Hu1703He could not be confirmed by its isozyme phenotype which was identical to the T24 phenotype. RFLP analysis and isozyme analysis revealed that three cell lines, Hu456, Hu549, and Hu961a, and two transformed sublines, HCV-29Tmv and Hu609Tmv, are sublines of T24. A common origin of Hu456, Hu549, Hu961a, HCV-29Tmv, and Hu609Tmv was confirmed by marker chromosome analysis. However, the T24 origin of these cytogenetically related cell lines was not supported by chromosome analysis of T24. RFLP analysis and HLA phenotyping of two tumorigenic and invasive sublines isolated from a culture of non-tumorigenic Hu609 cells showed that non-tumorigenic Hu609 cells can transform 'spontaneously' in vitro into tumorigenic Hu609T cells. The results emphasise the need for careful monitoring and screening of cell lines for their identity using more than one identification parameter.

Cell Line↗
PubMed1993

[Erosion of the uterine artery--an unusual late complication 19 weeks after Cesarean section].

In a 30-year old para I, following uncomplicated Caesarean section in late pregnancy, recurrent haemorrhage occurred, which finally peaked as an arterial mass bleeding. The diagnosis of an arrosion of a large branch of the uterine artery was made by clinical and sonographic means. Therapy consisted in operative revision of the uterotomy and the uterus is saved. The possible causes of bleeding in the late puerperium are discussed.

Adult↗
PubMed1993

Effect of nitrous oxide on haematopoiesis in vitro: biochemical and functional features.

Prolonged exposure to nitrous oxide (N2O) can induce dyshaematopoiesis by causing a functional cobalamin-deficiency state through oxidation of methyl-cobalamin (vitamin B12). Herein, we demonstrate that N2O exposure of murine bone marrow cells in vitro results in both functional and biochemical perturbations. In haematopoietic and bone marrow stromal cells, N2O exposure results in a decrease in methionine synthetase activity with a corresponding increase in homocysteine efflux. In semisolid cultures, N2O inhibits colony formation by cells belonging to the colony forming unit in culture (CFU-C) compartment. In contrast, N2O-exposed stromal cell layers maintain the ability to bind and support the differentiation of haematopoietic progenitor cells upon reseeding. Together, these data suggest that the dyshaematopoiesis seen after exposure to N2O is mediated through a direct inhibitory effect on haematopoietic cells.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1993

Training and employment in hearing-impaired subjects at 20-35 years of age.

This study was undertaken in order to evaluate the training and the employment situation in a cohort of hearing-impaired subjects born between 1955 and 1970. A sample of 288 persons was collected from 33,352 consecutive patients with hearing thresholds > 20 dB HL in at least one pure-tone frequency (250-8000 Hz) in one (right/left) ear and all living in the city of Copenhagen at the time of data collection. The total sample of 288 persons was divided into two groups according to age at onset of their hearing impairment: group 1 comprised 165 persons with congenital/early acquired hearing loss (before 2 years of age); group 2 comprised 123 subjects with acquired hearing loss (after 2 years of age), acting as a reference group. A questionnaire was mailed to all 288 subjects meeting the inclusion criteria, achieving 218 responses (76%). The questionnaire evaluated the educational and employment situation and revealed significant differences, training within crafts being more common in group 1 in contrast to training at university level being more common in group 2. A frequency of 31%/29% respectively of unemployment at the time of the questionnaire was found in the two hearing-impaired groups, compared with 12% in an age-matched background population. A subdivision according to hearing thresholds indicated that the degree of hearing loss is of importance for education at university level. A question concerning general well-being showed that the majority of hearing-impaired persons, irrespective of age of onset of their hearing impairment, are satisfied with their life.

Adolescent↗
PubMed1993

Methionine synthase inactivation by nitrous oxide during methionine loading of normal human fibroblasts. Homocysteine remethylation as determinant of enzyme inactivation and homocysteine export.

Nitrous oxide inactivates the enzyme methionine synthase by oxidation of enzyme bound cobalamin, which is formed from the cofactor methylcobalamin during the catalytic cycle. The resulting inhibition of homocysteine remethylation increases the homocysteine efflux and thereby the level of extracellular homocysteine, both in patients and cultured cells. In the present work we measured the kinetics of enzyme inactivation and homocysteine export rate in two human fibroblast cell lines exposed to nitrous oxide and cultured in the presence of low to supraphysiological concentrations (15-100 microM) of methionine. Both the rate and extent of methionine synthase inactivation were reduced by increasing methionine concentration in the culture medium. In cells not exposed to nitrous oxide, methionine increased the homocysteine export rate in a dose-dependent manner. Nitrous oxide increased the export at low methionine concentrations, so that for treated cells the export was high and essentially independent of the extracellular methionine level. Neither methionine nor nitrous oxide significantly affected the amount of S-adenosylmethionine or folate in these cells. These data agree with methionine synthase as a low Km and methionine conserving enzyme, highlight the importance of methionine synthase activity as a determinant of homocysteine export and point to the possibility of protecting the enzyme by reducing catalytic turnover through product inhibition.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1992

New rapid test for prenatal detection of trisomy 21 (Down's syndrome): preliminary report.

OBJECTIVE: To devise and evaluate a rapid screening method for detecting trisomy 21 (Down's syndrome) in samples of uncultured amniotic fluid cells. DESIGN: Non-radioactive in situ hybridisation with HY128, a 500,000 base pair yeast artificial chromosome probe specific for chromosome 21. Blinded study of 12 karyotypically normal amniotic fluid samples and eight samples trisomic for chromosome 21. SETTING: Cytogenetic and obstetric services at a tertiary referral centre, Copenhagen. MAIN OUTCOME MEASURES: Time necessary to complete the test. Proportion of cell nuclei containing two and three hybridisation signals in karyotypically normal and abnormal amniotic fluid samples. RESULTS: The test could be completed within three to four days after amniocentesis. In the normal samples a mean of 73% (range 61-82%) of the amniotic cell nuclei showed two hybridisation signals and 6% (0-18%) showed three signals. By contrast, among the trisomic samples 29% (19-38%) of the nuclei exhibited two signals and 48% (31-60%) showed three signals. CONCLUSION: The technique clearly distinguished between normal and trisomic samples. Prenatal diagnosis with in situ hybridisation with chromosome specific probes was fast and may make it possible to screen for selected, aneuploidies. However, the technique is still at a preliminary stage and needs further evaluation and refinement.

Amniocentesis↗
PubMed1992

[Non-radioactive in situ hybridization with chromosome-specific probes].

Non-radioactive in situ hybridization (ISH) is a relatively new and sensitive method for analysis of chromosome aberrations. ISH may be performed on metaphase spreads or directly on interphase cells. By means of ISH, the so-called probes are bound to well-defined regions on the chromosomes of a cell. After a visualization process the probes and thus indirectly the chromosome regions may be observed in a microscope. Chromosome-specific probes become bound to chromosomal DNA segments which are specific for certain groups of chromosomes or only for a single chromosome. The chromosome-specific probes may be subdivided into 1) repetitive probes which are bound at or around the centromere, 2) painting probes which are bound to a certain chromosome in its entire extent or to a limited segment of this and 3) locus-specific probes which are bound to a single unique DNA sequence in the genome. ISH with chromosome-specific probes is of great scientific significance for chromosomal localization of genes. It is to be anticipated that this technique may be employed clinically e.g. in prenatal diagnosis and in the diagnosis of cancer and viruses.

Chromosome Aberrations↗
PubMed1992

Comparison of structure and activities of peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus.

Initial structural and kinetic data suggested that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus were similar. Therefore they were characterized more fully. The three peroxidases were purified to RZ 2.5 and showed immunochemical identity as well as an identical M(r) of 38,000, pI about 3.5 and similar amino acid compositions. The N-termini were blocked for amino acid sequencing. The peroxidases had similar retention volumes by anion-exchange and gel-filtration chromatography. All peroxidases showed multiple peaks by Concanavalin A-Sepharose chromatography. The Concanavalin A-Sepharose profiles were different and depended furthermore on a fermentation batch. Tryptic peptide maps were very similar except for one peptide. This peptide contained an N-linked glycan composed of varying ratios of glucosamine and mannose for the three peroxidases. Rate constants and their pH dependence were the same for the three peroxidases using guaiacol or iodide as reducing substrates. We conclude that peroxidases from Coprinus cinereus, Coprinus macrorhizus and Arthromyces ramosus are most likely identical in their amino acid sequences, but deviate in glycosylation which, apparently, has no influence on the reaction rates of the enzyme. We suggest, that the Coprinus fungi express one peroxidase only in contrast to the lignin-degrading white-rot Basidiomycetes, which produce multiple peroxidase isozymes.

Amino Acid Sequence↗