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Biomedical subjects

C M Thomas

Publications and source records attributed to C M Thomas.

At least 145 records · Page 8Linked to original sources
PubMed1993

Multifunctional repressor KorB can block transcription by preventing isomerization of RNA polymerase-promoter complexes.

The KorB protein of broad-host-range plasmid RK2 is a transcriptional repressor involved in the control of genes for plasmid replication, conjugative transfer and stable maintenance. We have purified this protein close to homogeneity from cells harbouring an overexpression vector with the korB gene under the control of the tac promoter. KorB binds to restriction fragments bearing its proposed operator sequence, OB. Its interaction with this palindromic site was confirmed by DNaseI or hydroxyl radical footprinting at two OB sequences from RK2. Comparisons showed that the OB context affects the nature of the footprint. Our evidence suggests that KorB is a tetramer. As such, it may be able to bind two sites simultaneously on the same or on different DNA molecules. Using the korABF promoter, which is subject to KorB repression, we demonstrate by footprinting and restriction protection that KorB and RNA polymerase can bind simultaneously. Permanganate footprinting showed that KorB represses this promoter by preventing isomerization of the RNA polymerase-promoter complex from the closed to open form.

Bacterial Proteins↗
PubMed1993

Inhibition of proton-translocating transhydrogenase from photosynthetic bacteria by N,N'-dicyclohexylcarbodiimide.

The effects of N,N'-dicyclohexylcarbodiimide [(cHxN)2C] on the proton-translocating enzyme, NAD(P) H(+)-transhydrogenase (H(+)-Thase), from two species of phototrophic bacteria have been investigated. The polypeptides of H(+)-Thase from Rhodobacter capsulatus are membrane-associated, requiring detergent to maintain solubility. The enzyme from Rhodospirillum rubrum, however, has a water soluble polypeptide (Ths) and a membrane-associated component (Thm) which, separately, have no activity but which can be fully reconstituted to give a functional complex. Two observations suggest that (cHxN)2C inhibited H(+)-Thase from both species by modification either close to or at the NADP(H)-binding site on the enzyme: (a) the presence of NADP+ or NADPH caused increased inhibition by (cHxN)2C and (b) after treatment of the purified enzyme from Rb. capsulatus with (cHxN)2C, the release of NADP+ became rate-limiting, as evidenced by a stimulated rate of NADPH-dependent reduction of acetylpyridine adenine dinucleotide by NADH. Experiments in which Ths and Thm from R. rubrum were separately treated with (cHxN)2C then reconstituted with the complementary, untreated component revealed that the NADP(H)-enhanced modification by (cHxN)2C was confined to Thm. In contrast to some experiments with mitochondrial H(+)-Thase [Wakabayashi, S. & Hatefi, Y. (1987) Biochem. Int. 15, 667-675], there was no protective effect of either NAD+ or NADH on the inhibition by (cHxN)2C of enzyme from photosynthetic bacteria. However, amino acid sequence analysis of proteolytic fragments of Ths revealed that the NAD(H)-protectable, (cHxN)2C-reactive glutamate residue in mitochondrial H(+)-Thase might be replaced by glutamine in R. rubrum.

Amino Acid Sequence↗
PubMed1993

Synthesis and evaluation of 2-pyridinone derivatives as specific HIV-1 reverse transcriptase inhibitors. 3. Pyridyl and phenyl analogs of 3-aminopyridin-2(1H)-one.

In an ongoing effort to develop novel nonnucleoside, specific human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) inhibitors, a series of 3-[(pyridylmethyl)amino]- and 3-[(phenylmethyl)amino]-2-pyridinone derivatives was synthesized and tested for HIV-1 RT inhibitory activity. The more potent compounds have a 2'-methoxy group and 4'- and/or 5'-aliphatic substituents on the pyridyl and phenyl rings. Several of the more potent compounds were also evaluated for antiviral activity in MT-4 cell culture. From this series of compounds, 3-[N-[(5-ethyl-2-methoxy-6-methyl-3-pyridyl)methyl]amino]-5-ethyl-6- methylpyridin-2(1H)-one (6) was selected for clinical evaluation.

Aminopyridines↗
PubMed1993

Preelectrophoresis of agarose plugs containing bacterial chromosomal DNA prepared for analysis by pulsed field gel electrophoresis can improve the clarity of restriction patterns.

Pulsed field gel electrophoresis has indicated that chromosomal DNA isolated from stationary phase Pseudomonas fluorescens, Pseudomonas putida, and Escherichia coli cells immobilized in agarose can be fragmented during its release. For P. fluorescens it was demonstrated that the entire chromosome is affected and that there are no specifically fragile sites. The extent of the damage increased both during storage of the DNA and also when magnesium ions were provided, suggesting that nucleases may be involved. Chromosomal DNA isolated from exponentially growing cultures was subjected to significantly less damage during release and storage. Removal of damaged DNA by electrophoresis prior to digestion was shown to result in clearer restriction patterns of chromosomal DNA.

Chromosomes, Bacterial↗
PubMed1993

Identification of patients with persistent trophoblastic disease by means of a normal human chorionic gonadotropin regression curve.

OBJECTIVE: Data from the Dutch Central Registry of Hydatidiform Mole were used to establish a reference human chorionic gonadotropin regression curve after molar pregnancy. STUDY DESIGN: A normal serum human chorionic gonadotropin regression corridor was constructed after fitting data from 130 patients with uneventful human chorionic gonadotropin regression after evacuation of a complete hydatidiform mole. Retrospectively, data from 77 patients with persistent trophoblastic disease were analyzed by means of this normal corridor. Measurements were performed with a radioimmunoassay for both native and free human chorionic gonadotropin beta-subunits. RESULTS: Human chorionic gonadotropin disappearance curves showed a biphasic decline with median serum half-lives of 1.8 and 12.8 days. Median time until normalization was 74 days (range 28 to 430). With the 95th percentile line, 71 of 77 patients (92%) with persistent trophoblastic disease could be identified. In > 50% of cases this could be achieved within 6 weeks from evacuation. CONCLUSION: The normal regression corridor allows identification of patients with persistent trophoblastic disease and an expectant attitude within the limits of the corridor.

Chorionic Gonadotropin↗
PubMed1993

Study on the presence of homocysteine in ovarian follicular fluid.

OBJECTIVE: To study the presence of homocysteine, methionine and the vitamins folate, B12, and B6 in human ovarian follicular fluid (FF). DESIGN: Measurement of homocysteine, methionine, folate, and vitamins B12 and B6 in ovarian FF and blood. SETTING: Academic Department of Obstetrics and Gynecology at St. Radboud Hospital, Nijmegen, The Netherlands. PARTICIPANTS: Fourteen healthy women undergoing an IVF program. RESULTS: Detectable amounts of homocysteine and methionine were found in FF. Homocysteine concentrations were similar to those in serum. Methionine concentrations proved to be slightly but significantly lower than in corresponding serum samples. Concentrations of vitamins B12 and B6 were significantly lower in FF than in serum, whereas folate concentrations were not significantly different. A statistically significant correlation between corresponding serum and FF concentrations of homocysteine, folate, and vitamin B12 could be established. CONCLUSIONS: These data support the hypothesis that the ovum might be exposed to high homocysteine or low methionine concentrations, or both, and a lack of vitamins, which might be important in fertilization and early embryogenesis.

Adult↗
PubMed1993

CA 125 serum levels in the early post-operative period do not reflect tumour reduction obtained by cytoreductive surgery.

In order to assess whether CA 125 serum levels reflect the outcome of cytoreductive surgery, CA 125 antigen levels were determined prior to and after debulking surgery in 50 ovarian cancer patients and compared to CA 125 serum levels before and after surgery in a control group of 140 patients undergoing laparotomy for various malignant or benign diseases. A significant CA 125 decrease in the first post-operative week was seen in 56% of ovarian cancer patients whereas 26% remained stable and 18% showed a significant increase after surgery. Although removal of tumour had been complete in all 14 stage I-II ovarian carcinomas, only 2 of these patients showed a subsequent significant CA 125 decrease after cytoreductive surgery, while 4 patients showed a significant increase. Such increases of CA 125 following surgery were also seen in uterine carcinomas (30%), in gastrointestinal carcinomas (75%) and in patients after laparotomy for benign gynaecological diseases (23%). CA 125 pre-treatment levels were significantly lower in patients with post-operative increases than in patients with stable or decreasing CA 125 patterns. Patients with stable CA 125 levels also had lower CA 125 pretreatment levels compared to patients with a post-operative CA 125 decrease. Post-operative increases were observed for at least 2 weeks after debulking in the case of ovarian cancer. Pre-operative levels of these patients were either within the normal range or moderately elevated. Serial measurements during surgery in partial debulking showed a rapid CA 125 decline within 24 h followed by increasing CA 125 values thereafter. Our data indicate that CA 125 serum levels in the direct post-operative period do not always reflect the outcome of cytoreductive surgery. There appears to be an effect on CA 125 levels caused by the abdominal surgical procedure itself. Consequently, CA 125 levels after abdominal surgery should be interpreted with caution.

Adult↗
PubMed1993

Periconceptional vitamin profiles are not suitable for identifying women at risk for neural tube defects.

Folic acid and other vitamin deficiencies may play a role in the etiology of neural tube defects. The Medical Research Council Vitamin Study confirmed the beneficial effect of folic acid supplementation on the prevention of neural tube defects. However, the concentrations of vitamins other than folate were not a common feature of any of the former studies. We measured the concentrations of vitamin A, riboflavin, riboflavine-5'-monophosphate, flavine-adenine-dinucleotide, vitamin B-6, vitamin B-12, vitamin C, vitamin E, folate and ferritin in the serum of women who had previously had a child with a neural tube defect and were planning a further pregnancy. Vitamin and folic acid supplements were supplied before conception to 44 high risk women before conception. Eighteen other high risk women not given supplements were the control group. We concluded that vitamin profiles do not form a suitable means for identifying women at risk for neural tube defects before pregnancy. This endorses the hypothesis that the beneficial effect of folic acid supplementation on the prevention of neural tube defects is possibly at least partly due to the fact that it overrides a relative folic acid shortage caused by a metabolic disorder.

Ascorbic Acid↗
PubMed1993

Different follicle stimulating hormone/luteinizing hormone ratios for ovarian stimulation.

The aim of the present study was to investigate whether reducing the amount of luteinizing hormone (LH) in gonadotrophic preparations impairs follicular growth in in-vitro fertilization (IVF) cycles during suppression of endogenous LH levels. A selected group of 20 IVF patients was randomly divided into two groups. One group was treated with Org 31338 [follicle stimulating hormone (FSH)/LH 3:1], the other group with Metrodin (purified FSH), both during pituitary down-regulation with buserelin. A fixed daily dose of 150 IU FSH i.m. was given. Serum concentrations of FSH, LH, oestradiol and progesterone were determined frequently and serial ultrasound examinations were performed. Multiple follicular growth with concomitant rise of oestradiol levels was observed in all cycles. The duration of the stimulation phase was shorter in the group treated with Org 31338 than in the group treated with Metrodin. The number of follicles and oocytes and the fertilization rate was larger and the mean embryo quality was higher in the Org 31338 group, but the differences did not reach statistical significance. No significant differences were found in hormonal values. In women with normal endocrine profiles, lowering of the LH activity in gonadotrophic preparations during gonadotrophin-releasing hormone agonist treatment results in adequate ovarian stimulation. However, a preparation with some LH needed a shorter stimulation than a purified FSH preparation. Whether the other beneficial effects of Org 31338 also occur in a larger population needs further investigation.

Adult↗
PubMed1993

The ancestral IncP replication system consisted of contiguous oriV and trfA segments as deduced from a comparison of the nucleotide sequences of diverse IncP plasmids.

In most plasmids which have been studied to date the functions required for plasmid replication are clustered in a 2-3 kb region. However, in all known naturally occurring plasmids of the Escherichia coli incompatibility group P the essential replication functions, oriV, the vegetative replication origin and trfA, which encodes proteins essential to activate oriV, are separated by blocks of DNA consisting of either known genes conferring resistance to antimicrobial agents and/or putative transposable elements. Nucleotide sequence comparisons reported here reveal that these blocks of DNA have inserted at different points into a backbone of DNA common to IncP plasmids. The results indicate that in the common ancestor of present IncP plasmids oriV and trfA must have been contiguous, whilst a rho-independent transcriptional terminator, now lost in IncP alpha plasmids, may have prevented trfA operon transcription from interfering with the activity of oriV.

Bacterial Proteins↗
PubMed1993

Alkali treatment for rapid preparation of plant material for reliable PCR analysis.

For plant genetics, it would be useful to monitor easily the segregation of different alleles using the polymerase chain reaction (PCR). Preparation of DNA templates from individual plants needs to be rapid and reliable. A one tube protocol is described that involves subjecting plant tissue pieces to alkali, neutralization and heat denaturation prior to PCR analysis, and that proved to be much faster and more reliable than published protocols.

Alkalies↗
PubMed1993

Sub-50 oral contraceptives affect folate kinetics.

The effects of long-term use of oral contraceptives containing less than 50 micrograms of estrogen (sub-50 OCs) on the kinetics of folic acid monoglutamate, vitamin B12 levels, and iron status have been studied in 29 OC users (Marvelon) and in 13 women without OC use serving as controls. At 210 min after oral folate loading the median serum folate concentration was significantly lower in OC users when compared to the control group. OC users showed significantly higher total iron binding capacity and significantly lower serum vitamin B12 concentrations. This data demonstrates that sub-50 OCs significantly affect folate kinetics and vitamin B12 levels. However, the folate and vitamin B12 status does not seem to be at risk.

Adult↗
PubMed1993

Differences in serum lipids, lipoproteins, sex hormone binding globulin and testosterone between the follicular and the luteal phase of the menstrual cycle.

Fifty-four healthy women were studied during the follicular and the luteal phase of one menstrual cycle to determine possible cyclic influences on several parameters. After a 12-h overnight fast, blood samples were obtained between 08.00 h and 09.30 h and processed for total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoproteins A-I and B and total triglycerides. In the same samples we also measured serum concentrations of follicle-stimulating hormone, luteinizing hormone, 17 beta-oestradiol, progesterone, sex hormone binding globulin and testosterone. Serum total cholesterol, low-density lipoprotein cholesterol and the related apolipoprotein B were decreased significantly with 0.35 mmol/l, 0.44 mmol/l and 15 mg/l, respectively, during the luteal phase as compared to the follicular phase (p < or = 0.01). The ratios of low-density lipoprotein cholesterol/high-density lipoprotein cholesterol and of total cholesterol/high-density lipoprotein cholesterol were also significantly lower (p < 0.01) in the luteal phase because high-density lipoprotein cholesterol and its major carrier apolipoprotein A-I as well as serum triglycerides remained unchanged in the two cycle phases compared. Sex hormone binding globulin was significantly higher (p < 0.001) in the luteal phase than in the follicular phase of the investigated cycles, whereas serum testosterone remained unchanged in the two cycle phases compared. Therefore, the free androgen index decreased in the luteal phase (p < 0.01). These results indicate the necessity to define the cycle phase in which blood has been collected during control cycles in studies concentrating on possible effects of oral contraceptives or other administered sex steroids on serum lipids, lipoproteins and androgen metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Hyperhomocysteinemia: a risk factor in women with unexplained recurrent early pregnancy loss.

OBJECTIVE: To establish the prevalence of hyperhomocysteinemia in women with unexplained recurrent early pregnancy loss. DESIGN: In a patient-control study, the methionine-homocysteine metabolism was investigated by a standardized oral methionine-loading test. SETTING: Gynecologic outpatient department of university hospital. PATIENTS: One-hundred and two women who had been referred to the hospital because they suffered from at least two consecutive unexplained spontaneous abortions (study group) as well as 41 controls who were recruited by public advertisement were selected. INTERVENTIONS: Blood samples were collected just before and 6 hours after oral methionine administration to determine plasma total homocysteine concentrations. MAIN OUTCOME MEASURE: Plasma total homocysteine concentrations 6 hours after methionine loading. Hyperhomocysteinemia was defined as total homocysteine concentration at 6 hours exceeding the 97.5 percentile level of the controls. RESULTS: Hyperhomocysteinemia was diagnosed in 21 women of the study group (21%). In the parous women of the study group, the prevalence of hyperhomocysteinemia was more than two times greater compared with the nulliparous subjects (33% and 14%, respectively). CONCLUSION: Hyperhomocysteinemia is a risk factor in women with unexplained recurrent early pregnancy loss.

Abortion, Habitual↗
PubMed1993

The effects of periconceptional folic acid and vitamin supplementation on maternal folate levels and on neurulating hamster embryos in vivo.

We studied the effects of periconceptional oral supplementation of folic acid and vitamins on the maternal red blood cell (RBC) folate level of golden hamsters (Mesocricetus auratus, Waterhouse). The effects of folate deficiency and supplementation on the process of neurulation and the incidence of resorptions were evaluated. Groups of at least eleven mature virgin female hamsters were placed on one of six specific regimens which started two weeks prior to mating and continued until sacrifice on day nine of pregnancy. Just prior to sacrifice, blood samples were drawn by cardiac puncture to measure maternal folic acid levels in red blood cells. The staging of the embryos was based on O'Rahill's modification of Streeter's developmental horizons in human embryos. Considerable variation was observed in the stage of embryonic development of 9-day-old hamster embryos, both between littermates and between litters of the same gestational age. A high overall incidence of open neural tubes was observed, which did not reflect neural tube closure failures. A folate-free diet caused retardation of the embryonic development, although maternal folate levels were unaffected (p < 0.01). The RBC folate levels in the animals which received oral supplementation with folic acid was significantly higher than that in the unsupplemented controls (p < 0.001). Folic acid supplementation alone increased the RBC folate level significantly more than combined supplementation with multivitamins (p < 0.001). The data indicate that oral supplementation with folic acid and/or multivitamins produce adequate maternal RBC folate levels. An inadequate maternal folate intake can affect the growth of neurulating embryos even if the maternal RBC folate levels are still sufficient.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗