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Biomedical subjects

K Stevenson

Publications and source records attributed to K Stevenson.

54 records · Page 3Linked to original sources
PubMed1991

Human plasma lecithin:cholesterol acyltransferase. Preparation and use of immobilized p-aminophenylarsenoxide as a catalytic site-directed covalent ligand in enzyme purification.

A method is described for the preparation of p-aminophenylarsenoxide-linked carboxymethyl (CM) Bio-Gel A and its use as a specific, catalytic site-directed affinity chromatography ligand in the final stages of the purification of human plasma lecithin:cholesterol acyltransferase (LCAT) (EC 2.3.1.43). Previous mechanistic studies by us demonstrated that phenylarsenoxide derivatives, which are highly specific for vicinal thiols, could inhibit LCAT via a covalent interaction with the sulphydryl groups of the two catalytic cysteine residues and that this inhibition could be rapidly and completely reversed upon addition of 2,3-dimercaptopropanesulphonic acid. The ligand was covalently linked to CM Bio-Gel A activated through an N-hydroxysuccinyl ester formed by N-hydroxysuccinimide and dicyclohexylcarbodiimide in dry dimethyl sulphoxide; 87% of the added p-aminophenylarsenoxide was coupled to the CM Bio-Gel A in 3 h at 25 degrees C giving 2.3 mg of p-aminophenylarsenoxide per ml of gel. Homogeneous LCAT free of apo A-I, apo E, apo D and albumin was obtained in an 11% yield and purified 15,013-fold overall. A 13-fold purification was obtained by chromatography upon p-aminophenylarsenoxide-CM Bio-Gel A. This method is a useful final step in LCAT purification and will prove valuable in the purification of other proteins and compounds containing vicinal thiols.

Arsenicals↗
PubMed1991

Glycaemic control in adolescents with type I diabetes and parental expressed emotion.

The parents of 34 adolescents with type I diabetes were interviewed using the Camberwell Family Interview, a well validated and reliable standardised interview which measures aspects of family interaction previously reported as important in the families of diabetics. Contrary to predictions from previous research, poor glycaemic control was not associated with parental apathy, criticism of the child with diabetes, or marital discord. Greater emotional involvement by parents was associated with good glycaemic control. Overall, there was close agreement between parents in their responses although mothers showed more accurate appraisal of their child's diabetes than did fathers.

Adolescent↗
PubMed1990

The incidence of hyponatremia during prolonged ultraendurance exercise.

Recent studies have shown that potentially fatal hyponatremia can develop during prolonged exercise. To determine the incidence of hyponatremia in athletes competing in ultradistance events, we measured serum sodium levels in 315 of 626 (50%) runners who were treated for collapse after two 90 km ultramarathon footraces (total starters 20,335; total finishers 18,031) and in 101 of 147 (69%) finishers in a 186 km ultratriathlon. In both races the athletes drank fluids with low sodium chloride content (less than 6.8 mmol.l-1). Hyponatremia (serum sodium level less than 130 mmol.l-1) was identified in 27 of 315 (9%) collapsed runners in the 90 km races and in none of the triathletes. In response to diuretic therapy, the runner with the most severe hyponatremia (serum sodium level = 112 mmol.l-1) excreted in excess of 7.5 l dilute urine during the first 17 h of hospitalization. These data suggest that, although symptomatic hyponatremia occurs in less than 0.3% of competitors during prolonged exercise even when they ingest little sodium chloride, it is found in a significant proportion (9%) of collapsed runners. A regulated contraction of the extracellular fluid volume would explain why the majority of athletes maintain normal serum sodium levels even though they develop a significant sodium chloride deficit during prolonged exercise. Alternatively, sodium chloride losses during prolonged exercise may be substantially less than are currently believed. Physicians treating collapsed ultradistance athletes need to be aware that as many as 10% or more of such patients may be hyponatremic.

Exercise↗
PubMed1989

The human cytochrome P450 CYP3 locus: assignment to chromosome 7q22-qter.

The cytochrome P-450s are a large multigene family of enzymes involved in the metabolism and detoxification of drugs and chemicals. Using a full length cDNA clone for the human nifedipine oxidase gene (CYP3) and a panel of human-rodent somatic cell hybrids, we have assigned this gene family to chromosome 7q22-qter. A search for RFLPs using this probe yielded no results.

Animals↗
PubMed1989

Cervical carcinoma and human cytomegalovirus.

Human cytomegalovirus (HCMV) is a sexually transmitted virus which has been implicated in both cervical cancer and its precancerous state, cervical intraepithelial neoplasia (CIN). The evidence for this and the current possible mechanisms by which HCMV could be involved are discussed at the molecular level.

Animals↗
PubMed1989

Mesectodermal leiomyoma of the ciliary body: case report.

The clinical, light microscopical, and electron microscopical features of a mesectodermal leiomyoma of the ciliary body are presented. This exceptionally rare and apparently benign tumour is considered to be of neural crest origin. In the case described the tumour cells were seen to contain thin filaments with focal densities and conspicuous numbers of mitochondria, and smooth muscle protein was demonstrated by immunohistochemical means.

Adult↗
PubMed1988

Regulation of phenobarbital-inducible cytochrome P-450s in rat and mouse liver following dexamethasone administration and hypophysectomy.

Cytochrome P-450s are a superfamily of haem-containing proteins involved in the metabolism of foreign compounds, as well as a variety of endogenous molecules. The hepatic levels and function of this diverse group of enzymes are determined by both constitutive and xenobiotic regulators. To examine the role of constitutive factors in cytochrome P-450 regulation, the levels of three distinct groups of phenobarbital-inducible hepatic cytochrome P-450s were studied following dexamethasone-treatment or hypophysectomy. In the mouse, dexamethasone was a potent inducer of proteins within the PB1 (subfamily IIC), PB2c (family III) and PB3 (subfamily IIB) families. These findings were strikingly different from the effects in the rat where essentially no effect on PB3 expression and indeed suppression of proteins related to PB1 was observed. Determination of mRNA concentration indicated that the difference was at the level of transcription. These findings indicate that synthetic glucocorticoids have the potential to be potent phenobarbital-like inducing agents. In the mouse hypophysectomy, like dexamethasone, induced hepatic mRNA of P-450 from families P-450IIB, P-450IIC and P-450III. Again a species difference was observed as this treatment had essentially no effect in the rat. These data in the mouse indicate that factors produced in the pituitary can either affect the transcription rate of phenobarbital and dexamethasone-inducible P-450 genes or influence the stability of their mRNAs.

Animals↗
PubMed1987

Transfer function analysis of the autonomic response to respiratory activity during random interval breathing.

We report a new method for the noninvasive characterization of the frequency response of the autonomic nervous system (ANS) in mediating fluctuations in heart rate (HR). The approach entails computation of the transfer function magnitude and phase between instantaneous lung volume and HR. Broad band fluctuations in lung volume were initiated when subjects breathed on cue to a sequence of beeps spaced randomly in time. We studied 10 subjects in both supine and standing positions. The transfer function, averaged among all the subjects, showed systematic differences between the two postures, reflecting the differing frequency responses of the sympathetic and parasympathetic divisions of the ANS.

Adult↗
PubMedDate not supplied

A gene therapy/targeted radiotherapy strategy for radiation cell kill by.

BACKGROUND: Although [131I]meta-iodobenzylguanidine (MIBG) is currently one of the best agents available for targeted radiotherapy, its use is confined to a few neural crest derived tumours which accumulate the radiopharmaceutical via the noradrenaline transporter (NAT). To determine whether this drug could be used for the treatment of non-NAT expressing tumours following genetic manipulation, we previously showed that plasmid mediated transfection of NAT into a non-NAT expressing glioblastoma cell line, UVW, endowed the host cells with the capacity to actively accumulate [131I]MIBG. We now present data defining the conditions required for complete sterilisation of NAT transfected cells cultured as multicellular spheroids and treated with [131I]MIBG. METHODS: NAT transfected UVW cells, grown as monolayers and spheroids, were treated with various doses of [131I]MIBG and assessed for cell kill by clonogenic survival and measurement of spheroid volume over time (growth delay). Spheroids were left intact for different time periods to assess the effect of radiation crossfire on cell death. RESULTS AND CONCLUSIONS: Total clonogen sterilisation was observed when the cells were grown as three-dimensional spheroids and treated with 7 MBq/ml [131I]MIBG. The added benefit of radiation crossfire was demonstrated by the improvement in cell kill achieved by prolongation of the maintenance of [131I]MIBG treated spheroids in their three-dimensional form, before disaggregation and clonogenic assay. When left intact for 48 h after treatment, spheroid cure was achieved by exposure to 6 MBq/ml [131I]MIBG. These results demonstrate that the efficiency of cell kill by [131I]MIBG targeted therapy is strongly dependent on beta-particle crossfire irradiation. This gene therapy/targeted radiotherapy strategy has potential for [131I]MIBG mediated cell kill in tumours other than those derived from the neural crest.

3-Iodobenzylguanidine↗
PubMedDate not supplied

Transfectant mosaic spheroids: a new model for evaluation of tumour cell killing in targeted radiotherapy and experimental gene therapy.

BACKGROUND: We describe an in vitro tumour model for targeted radiotherapy and gene therapy that incorporates cell population heterogeneity. MATERIALS AND METHODS: Transfectant mosaic spheroids (TMS) and transfected mosaic monolayers (TMM) are composed of two cell populations derived from a single cell line. The cells of one population were transfected with the noradrenaline transporter gene (NAT), allowing active uptake of a radiolabelled targeting agent meta-[131I]iodobenzylguanidine ([131I]MIBG); the other population of cells was derived from the same parent line and transfected with a marker gene - green fluorescent protein (GFP). After treatment with [131I]MIBG, cell kill was determined in TMM by clonogenic assay and in TMS by clonogenic assay and spheroid growth delay. RESULTS: We have used the TMS model to assess the 'radiological bystander effect' (radiation cross-fire) conferred by the beta-emitting radiopharmaceutical [131I] MIBG whose cellular uptake is facilitated by the transfected gene encoding NAT. We show that cell killing by [131I]MIBG in both TMS and TMM cultures increased in direct proportion to the fraction of NAT-transfected cells and that the degree of cell killing against fraction transfected was greater in TMS, suggestive of a greater bystander effect in the three-dimensional culture system. CONCLUSIONS: TMS provide a useful model for assessment of the effectiveness of targeted radiotherapy in combination with gene therapy when less than 100% of the target cell population is expressing the NAT transgene. Further, this novel model offers the unique opportunity to investigate radiation-induced bystander effects and their contribution to cell cytotoxicity in radiotherapy and other gene therapy applications.

3-Iodobenzylguanidine↗
PubMedDate not supplied

Using content analysis of video-recorded consultations to identify smokers' "readiness" and "resistance" towards stopping smoking.

Although physicians' brief advice against smoking is effective in helping smokers to stop, very little is known about the process of counseling smokers. We describe the development of a coding system for describing smokers' motivation to stop smoking as judged by their behaviour when discussing smoking with their family physician. We analysed video-recordings of consultations between 47 self-reported smokers and 29 family physicians where smoking was discussed. By a process of observing recordings, reading transcripts and discussion, we developed a coding system for describing smokers' levels of motivation to stop smoking. This consists of four behaviours thought to indicate "readiness" (higher motivation to stop) and four "resistance" (lower motivation to stop). Interobserver reliability between two observers was good (Kappa = 0.71 for readiness, 0.73 for resistance behaviours). We discuss the relevance of our descriptions for clinicians and the possibility of developing this work further to enable systematic research into doctor-patient interactions where smokers are counseled to stop.

Attitude to Health↗
PubMedDate not supplied

Detection of PCR products from Mycobacterium avium subspecies Paratuberculosis using oligonucleotides containing multiple 2,4-dinitrophenyl reporter groups.

A pool of five oligonucleotides has been used to detect the pathogenic organism Mycobacterium avium subspecies paratuberculosis in PCR-amplified DNA from ruminants. The oligonucleotides were labelled at the 5'-end with three dinitrophenyl reporter groups and hybridised to the target DNA, which was fixed to a nylon membrane by ultraviolet irradiation. Colourimetric detection of the PCR product was carried out using an anti-DNP antibody conjugated to horseradish peroxidase or to alkaline phosphatase. Detection with alkaline phosphatase was more sensitive than with horseradish peroxidase but, in both cases, the PCR product could be easily detected. The DNP labelling system offers an economic and effective alternative to biotin, digoxigenin or fluorescein for the detection of PCR-amplified DNA.

Bacterial Typing Techniques↗