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Biomedical subjects

J Dawes

Publications and source records attributed to J Dawes.

At least 37 records · Page 2Linked to original sources
PubMed1993

Low molecular weight dermatan sulphate (Desmin 370) does not cross the ovine placenta.

Transplacental passage of the low molecular weight dermatan sulphate Desmin 370 was investigated in pregnant sheep, using 125I-labelled Desmin 370 to optimize the sensitivity of the study. Chronically catheterized cross-bred pregnant ewes at approximately 120 d gestation received 3700 kBq 125I-labelled Desmin 370 with 1 mg/kg carrier unlabelled Desmin 370 intravenously. Early clearance from the maternal circulation was biexponential, and the volume of distribution corresponded closely with the theoretical value for distribution in total body water. Soon after injection low levels of radioactivity were detected in the fetal circulation and accumulated over the next 2 h, so that as the concentration of 125I-Desmin 370 in the maternal circulation declined with time the fetal level of radiolabel rose to represent a significant concentration in relation to that in the mother. Radioactivity was also excreted into the fetal urine. However, while 50% of the radiolabelled material present in maternal plasma 150 min post-injection was intact Desmin 370 and the remaining 50% represented degradation products, fetal urine contained only these fragments. By contrast, intact Desmin 370 was readily excreted into fetal urine after direct introduction to the fetal circulation. Thus molecules of intact Desmin 370 with anticoagulant activity cannot cross the ovine placenta, and low molecular weight dermatan sulphates may be valuable for prophylaxis and treatment of thrombotic disease during pregnancy.

Animals↗
PubMed1993

Interactions of heparins in the vascular environment.

Heparins are exposed in vivo to a complex environment containing heparin-binding proteins in solution, on the surface of cells and in the extracellular matrix. However, most studies of heparin binding have been carried out in simplified systems which fail to address the competition for binding resulting both from the different concentrations of constituent proteins and their relative affinities for heparin. In the blood heparin binds to platelets in a saturable, specific and reversible interaction which occurs in the presence of competing plasma proteins and which may be prothrombotic. Similar binding to monocytes and endothelial cells occurs but has not yet been confirmed in whole blood. Such interactions could inhibit coagulation resulting from generation of tissue factor activity and modulate endothelial responses which affect coagulation, fibrinolysis and cell growth as well as representing a physiologically significant anti-inflammatory function of heparin. Low-molecular-weight (LMW) heparins have lower affinities than unfractionated heparin for all cell receptors studied and are less likely to exert their effects through cellular interactions. In whole plasma in the absence of platelet release, antithrombin III was the most abundant protein bound to therapeutic doses of unfractionated heparin, and histidine-rich glycoprotein its only effective competitor, while both histidine-rich glycoprotein and vitronectin were potentially important modulators of LMW heparin activity. Sequestration of vitronectin and complement factor H by immobilised heparins could promote an effective defence against complement-mediated prothrombotic activity and cell damage under physiological conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Blood viscosity, fibrinogen, and activation of coagulation and leukocytes in peripheral arterial disease and the normal population in the Edinburgh Artery Study.

BACKGROUND: Increased blood and plasma viscosity, hematocrit, fibrinogen, and activation of coagulation and leukocytes have been reported in patients with claudication; however, their associations with symptomatic and asymptomatic peripheral arterial disease have not been reported in an epidemiological study. METHODS AND RESULTS: Blood and plasma viscosity, hematocrit, fibrinogen, urinary fibrinopeptide A, plasma leukocyte elastase, and uric acid were measured in a random sample of 1,581 men and women aged 55-74 years in Edinburgh, Scotland, and related to peripheral arterial stenosis (ankle-brachial systolic pressure index, ABPI) and to lower limb ischemia (intermittent claudication and reactive hyperemia test). Each variable (except fibrinopeptide A) was significantly related to prevalent symptomatic and asymptomatic peripheral arterial disease. On multivariate analysis, blood viscosity (p < 0.05) and fibrinogen (p < 0.01) were independently associated with peripheral arterial narrowing (ABPI); a positive interaction was found between fibrinogen and smoking in the association with ABPI. Plasma viscosity was associated with claudication in the presence of a given degree of arterial narrowing (odds ratio of claudication in top quintile compared with bottom quintile of plasma viscosity, 3.35; 95% CI, 1.32, 8.51). Leukocyte elastase and uric acid were each associated with reactive hyperemia independently of arterial narrowing (p < 0.01). CONCLUSIONS: Blood rheological factors and leukocyte activation as well as arterial narrowing are associated with lower limb ischemia in the general population and may be implicated in its pathogenesis.

Aged↗
PubMed1992

Effects of heparin and endothelial cell growth supplement on haemostatic functions of vascular endothelium.

Heparin in combination with endothelial cell growth factor (ECGF) affects physiological responses and growth of human umbilical vein endothelial cells (HUVEC). We have examined the effect of heparin, crude ECGF (endothelial cell growth supplement [ECGS]), or both on the basal and thrombin challenged output of metabolites by HUVEC. The supernatant and/or cell lysate was assayed for released prostacyclin, von Willebrand factor, tissue plasminogen activator, plasminogen activator inhibitor and thrombospondin. Heparin modified release of all these metabolites when in combination with ECGS, and in general these responses were the opposite of those generated by inflammatory mediators such as interleukin-1. It has been postulated that heparin acts by potentiating the effect of ECGF, but heparin inhibited thrombospondin release and enhanced that of von Willebrand factor in the absence of ECGS, while ECGS alone inhibited release of plasminogen activator inhibitor. Thus, under our experimental conditions it would appear that heparin and crude ECGF can affect HUVEC independently of one another.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Human vascular endothelial cells catabolise exogenous glycosaminoglycans by a novel route.

Heparin and other anticoagulant glycosaminoglycans were radiolabelled with 125I and their catabolism by human vascular endothelial cells in culture was studied. Heparin, heparan sulphate and pentosan polysulphate were associated with the cellular fraction and incorporated into the subendothelial matrix, but dermatan sulphate was not found in either fraction. High molecular weight, fully desulphated carbohydrate chains were major catabolic products of all those glycosaminoglycans which were taken up by the cells. Pentosan polysulphate was not degraded further, but the catabolism of heparan sulphate, and to a lesser extent that of heparin, also yielded small oligosaccharides. Thus the first step in catabolism of exogenous glycosaminoglycans by human vascular endothelial cells appears to be complete desulphation, which destroys their biological activity, followed by depolymerisation of the carbohydrate chain. This alternative to the sequential action of lysosomal exoenzymes is dependent upon binding to the cell; thus dermatan sulphate, which is not associated with the cellular fraction, is not catabolised.

Binding Sites↗
PubMed1992

Antithrombin III Budapest: a single amino acid substitution (429Pro to Leu) in a region highly conserved in the serpin family.

Antithrombin III (AT) is a major plasma serine protease inhibitor and a member of the serpin family of proteins. We have characterized the molecular and genetic basis of AT Budapest, an inherited variant of AT that is associated with thrombotic disease in affected family members. A single amino acid substitution, 429Pro to Leu, was identified, occurring in a region of the molecule that is highly conserved in members of the serpin family. Two forms of variant protein were present in approximately equal amounts in the plasma of the propositus, who is homozygous for the mutation. One form, which had apparently normal Mr, bound heparin strongly and retained some residual thrombin inhibitory activity. The other form had only weak heparin affinity and no antiproteinase activity, and had slightly decreased mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under nonreducing conditions; this normalized in the presence of a reducing agent, suggesting it was caused by a change in conformation. Additional support for a difference in conformation of the two forms of variant was provided by the finding that the fraction that bound heparin-Sepharose was recognized by a monoclonal antibody raised against normal AT, whereas the weak-affinity fraction was not.

Amino Acid Sequence↗
PubMed1992

Plasma concentrations of endogenous heparinoids in portal hypertension.

Bleeding as a complication of liver disease can occur in the absence of recognised haemostatic defects. It is now possible to measure the concentration of endogenous heparinoid substances in the blood using a competitive binding assay. One such substance, heparan sulphate (normal range < 600 ng/ml) was assayed in the plasma of 49 patients admitted because of oesophageal varices. In 27 patients with recent upper gastrointestinal bleeding the median plasma heparan sulphate value was 1700 ng/ml (interquartile (IQ) range 900-3900) compared with 390 ng/ml (IQ range 256-800) in 22 patients with no recent bleed (p < 0.01). As heparan sulphate is metabolised by the same route as exogenous heparin, an attempt to establish a cause for the raised heparan concentrations was made by measuring the clearance of exogenous heparin in 10 portal hypertensive patients and 10 controls. The median half life of heparin in plasma in the portal hypertensive patients (25.5 minutes; IQ range 22-34) was significantly longer (p < 0.007) than the median half life in the controls (18.7 minutes; IQ range 17-21.5). Thus, there is evidence of raised concentrations of endogenous heparin like substances in portal hypertensive patients after gastrointestinal bleeding. These high concentrations may result from reduced hepatic clearance.

Esophageal and Gastric Varices↗
PubMed1992

Neutrophil count and activation in vascular disease.

An elevated peripheral leucocyte count is associated with an increased risk of myocardial infarction and progression of coronary artery disease. The aim of this study was to determine neutrophil count and activation, measured as an increase in plasma neutrophil elastase, in patients with stable ischaemic heart disease, insulin-dependent diabetes mellitus and essential hypertension compared with a comparable group of control subjects. Neutrophil count and neutrophil elastase were raised significantly for patients with ischaemic heart disease (p less than 0.005; p less than 0.002), diabetes mellitus (p less than 0.001; p less than 0.01) and hypertension (p less than 0.05; p less than 0.0001) respectively compared to the control subjects. Neutrophil elastase did not correlate with subject age or leucocyte count. This study confirms the association between leucocyte count and vascular disease, and is consistent with neutrophil activation contributing to the progression of vascular disease.

Adult↗
PubMed1991

Novel affinity chromatographic system for the single-step purification of glycosaminoglycans from complex systems using volatile buffers.

A new system for the isolation and purification of glycosaminoglycans (GAGs) and related molecules from complex systems such as plasma is described. Affinity chromatography which exploits the very high affinity between the polymeric base Polybrene and sulphated polysaccharides was used. A novel volatile buffer system composed of ammonium formate and formic acid, which allows the complete recovery of samples, was developed, and elution conditions were optimised for the separation and purification of GAGs of different charge densities. Using this system the losses associated with dialysis and desalting, frequently necessary preliminaries to further analysis, are avoided.

Buffers↗
PubMed1991

Prognostic markers in diarrhoea-associated haemolytic-uraemic syndrome: initial neutrophil count, human neutrophil elastase and von Willebrand factor antigen.

The observed increase in plasma von Willebrand factor antigen (vWF:Ag) in patients with the haemolytic-uraemic syndrome is presumed to be secondary to endothelial damage, which is a central event in these diseases. As the prognostic value of such changes has not been previously evaluated, vWF:Ag has been measured in plasma from children reported to a national survey of haemolytic-uraemic syndrome. Human neutrophil elastase was also measured, as an initial neutrophilia has been shown to have prognostic value in diarrhoea-associated haemolytic-uraemic syndrome. Despite a significant elevation of plasma vWF:Ag concentration in these patients at presentation, the values did not correlate with the period of thrombocytopenia, the need for dialysis, or outcome. However, children with a poor outcome had significantly greater plasma elastase concentrations compared to those who had a good outcome.

Antigens↗
PubMed1991

No transplacental passage of standard heparin or an enzymatically depolymerized low molecular weight heparin.

In 21 women who had an abortion by hysterotomy between the 15th and 23rd week of pregnancy, the possibility that unfragmented heparin or low molecular weight heparin (LMWH) passed the placental barrier to the foetus was studied. Laboratory analyses included amidolytic assays of factor Xa inhibitory activity (XaI), antithrombin III (ATIII) and a direct measurement of heparin-like substances in plasma with a competitive binding assay. The ATIII concentration in foetal plasma was about 20% of that in normal human plasma and varied considerably between individuals (2-27%). The XaI activity did not differ between the two treated groups, but the mean XaI activity of the combined groups differed from zero (P less than 0.05). If the XaI activity was corrected for the ATIII concentration, the heparin activities no longer differed significantly from zero. As the concentration of heparin-like substances were above the detection limit (0.35 microgram/ml) in 6/16 analysable samples of foetal plasma, a further 15 women who had not received any heparin were included as controls. In 12/14 analysable foetal plasmas heparin-like substances in concentrations above 0.35 micrograms/ml could be detected. Determination of heparin activity in foetal plasma is thus difficult due to the influence of endogenous ATIII on heparin assays. In conclusion, this study did not demonstrate any evidence for the passage of heparin or LMWH across the placental barrier. No differences were detected whether unfragmented heparin or LMWH had been given to the mothers. Our results also indicate the presence of an endogenous glycosaminoglycan in foetal plasma.

Adolescent↗
PubMed1991

The pharmacokinetics of dermatan sulphate MF701 in healthy human volunteers.

1. The pharmacokinetics of dermatan sulphate MF701 were studied in 12 healthy males after administration of single intravenous bolus (200 mg), intramuscular (100 and 300 mg) and oral (1 g) doses. The study was conducted according to a within-subject crossover design in two paired blocks. 2. Plasma drug concentrations were measured using a competitive binding assay and a range of biological activity assays, including a sensitive catalysed thrombin inhibition test. 3. Following intravenous administration, plasma concentrations of dermatan sulphate determined by competitive binding assay were described by a two-compartment open model with an initial t1/2, in of 0.6 h and a t1/2,z of 7.5 h. Biological activity assays were insufficiently sensitive to detect the second phase, and therefore yielded apparent monoexponential kinetics. 4. After intramuscular injection the apparent bioavailability of dermatan sulphate was 16-20%. Plasma drug concentrations increased in proportion to dose when measured by competitive binding assay. Low concentrations persisted for more than 24 h at the higher dose, and these may prove therapeutically relevant on chronic administration. 5. We confirm that dermatan sulphate is the only glycosaminoglycan known to generate significant plasma concentrations following oral administration. Oral bioavailability was estimated to be 7%.

Adolescent↗
PubMed1991

Neutrophil activation is confined to the maternal circulation in pregnancy-induced hypertension.

The aim of this study was to determine whether neutrophil activation occurs in the fetal circulation in pregnancy-induced hypertension and to correlate this with evidence of neutrophil activation in the maternal circulation. Twenty-one normal pregnancies and 23 complicated by pregnancy-induced hypertension were studied in the third trimester. The mean length of gestation at delivery was significantly shorter (P less than .01) and the mean birth weight percentile was significantly lower (P less than .05) in the hypertensive group; otherwise the groups were comparable. Blood was obtained before cesarean delivery or established labor in the mothers and immediately after delivery from the umbilical vein. Plasma neutrophil elastase, which is released after neutrophil activation, was measured by radioimmunoassay as a marker for neutrophil activation. The mean (+/- standard error) concentration of neutrophil elastase in maternal plasma in the hypertensive group (35.9 +/- 4.7 ng/mL) was significantly higher than in the normal group (20.8 +/- 0.87 ng/mL) (P less than .005). The concentration of neutrophil elastase in umbilical venous plasma was not significantly different between the normal and hypertensive groups. However, significantly higher concentrations of neutrophil elastase were found in the umbilical venous plasma of pregnancies delivered vaginally compared with those delivered by cesarean (P less than .05) regardless of diagnosis. There was no correlation between maternal venous and umbilical venous plasma neutrophil elastase concentrations, birth weight percentile, plasma urate, or platelet count. These data suggest that neutrophil activation is confined to the maternal circulation in pregnancy-induced hypertension where it may contribute to vascular damage and dysfunction in areas such as the placental bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Granulocyte elastase levels do not correlate with anaerobic and aerobic bacterial growth in seminal plasma from infertile men.

Seminal culture and leucocyte elastase measurements were undertaken on samples from 30 men attending an infertility clinic. Elastase levels over 1000 ng ml-1 were obtained in 14 men and positive bacterial culture in 11 men, but there was no correlation between these two sets of measurements. While granulocyte elastase measurement in semen may reflect inflammation, our study suggests that it cannot be used as a simple marker of infection particularly in a population such as ours where the prevalence of prostatitis and genital infection is low.

Bacteria, Aerobic↗
PubMed1990

High molecular weight aggregate content of heated and unheated factor VIII products determined by fast-protein liquid chromatography.

The molecular-weight distribution of proteins in factor VIII concentrates has been analysed by fast-protein liquid chromatography. The proportion of high-molecular-weight (HMW) aggregates in one product increased on freeze-drying and heating, with fibrinogen and fibronectin being the main protein components of the HMW peak. In all other concentrates, the HMW peak was less than or equal to 5% of the total protein content and there were no differences in HMW content according to purity or method of viral inactivation.

Chromatography, Liquid↗
PubMed1990

Leucocyte mobilization and release of neutrophil elastase following acute insulin-induced hypoglycaemia in normal humans.

Insulin-induced hypoglycaemia in humans is associated with the rapid mobilization of leucocytes in peripheral blood. The aim of the present study was to determine whether neutrophil activation, manifested in plasma by neutrophil elastase concentration, occurs in response to insulin-induced hypoglycaemia. Acute hypoglycaemia (mean blood glucose 1.3 +/- 0.2 mmol l-1; mean +/- SD) was induced with intravenous insulin in 15 normal human subjects, and provoked an increase in the neutrophil count from 3.4 (range 1.9-6.5) to 10.7 (9.4-16.3) X 10(9) l-1 (p less than 0.001), and in the total leucocyte counts from 5.7 (4.1-8.1) to 12.8 (11.3-18.6) X 10(9) l-1 (p less than 0.001), with associated elevations in plasma neutrophil elastase concentration from 21 (12-34) to 29 (14-70) micrograms l-1 (p less than 0.05), and in total neutrophil elastase concentration from 5.90 (3.13-8.20) to 25.20 (23.00-52.00) mg l-1 (p less than 0.001). As neutrophil elastase is implicated in the development of vascular disease, this rise in response to hypoglycaemia may be of pathological importance in insulin-treated diabetic patients.

Adult↗