Biomedical subjects

A R Ewins

Publications and source records attributed to A R Ewins.

6 recordsLinked to original sources

PubMed1999

Physicochemical properties of arterial elastin and its associated glycoproteins.

Microfibrillar glycoproteins are a significant component of vascular elastic tissue, but little is known about their contribution to vascular physiology and pathology. We have investigated some physicochemical properties of the glycoproteins that may be pertinent to these roles. Because of the difficulty in isolating intact glycoproteins in a form and quantity suitable for physicochemical examination, we based our analysis on a comparison of the properties of porcine thoracic aorta and pulmonary artery extracted with GuHCl and collagenase (preparation GC) and after further treatment with dithioerythritol to remove glycoproteins (preparation GC/DTE). Amino acid analysis showed that GC/DTE had the amino acid composition of pure elastin while GC contained a higher proportion of polar amino acids, particularly in the aortic preparation. GC stained with alcian blue, particularly in the intimal region, but GC/DTE did not. GC had a higher water content and a slower viscoelastic response and the circumferential elastic modulus was approximately 50% lower (whether expressed in terms of sample weight or elastin content). Clearly, therefore, the microfibrils do not stiffen the network and may prevent the alignment of elastin fibers in the circumferential direction. Their effect on hydration may arise either because they impose mechanical constraints on the geometry of the network or because they modify the inter- and intramolecular hydrophobic or electrostatic interactions that influence the tissue organization and hydration. Molecular probe measurements of the intrafibrillar pore structure using radiolabeled and fluorescent probes showed that removal of the microfibrils caused a slight decrease in the extrafibrillar water space and a larger decrease in the intrafibrillar water space. Sucrose, a small probe molecule, was able to penetrate most of the intrafibrillar water space when microfibrils were present but was virtually excluded when they were not. Potentiometric titration and radiotracer assays of ion binding both showed that the microfibrils contribute a considerable negative charge (-9 mumoles/g wet tissue in the aortic preparation and -16 mumoles/g wet weight in the pulmonary artery) and increase calcium binding by approximately 30%.

Animals↗

PubMed1992

The polyelectrolyte properties of elastin.

The charge structure and ionic interactions of elastin prepared from the pig thoracic aorta by acid, alkali, or CNBr extraction have been investigated by potentiometric titration and radiotracer techniques. The number of charged groups was consistent with the amino acid composition, comparable to elastin from other sources and insensitive to the method of preparation. The enthalpies of ionization of the basic groups were comparable for those previously found for proteins but those of the acidic groups were higher. Ionic interactions were predominantly electrostatic although a strong affinity for chloride ions was noted. Changes in ionic interactions as the elastin was stretched had a similar effect to an increase in the apparent fixed charge density of the tissue. Mechanical strain altered the protonation of the elastin and the pK of the carboxyl groups. Conversely, the conformation of the elastin network varied with ionic strength and pH, being particularly sensitive to the degree of ionization of the more basic groups and with the ionic strength and anion composition of the medium. We speculate that strain induced changes in the conformation of elastin altering its reactivity towards lipids, ions or matrix macromolecules or changes in its mechanical properties resulting from changes in its ionic environment may be of physiological or pathological importance.

Animals↗

PubMed1988

The uptake of ions and neutral solutes by the artery and by artery wall preparations.

Radiotracer methods have been used to measure the distributions of inorganic ions in the aorta. Data on fresh tissue were generally consistent with previous measurements and showed UCa greater than UI greater than UNa. In order to relate these measurements to the macromolecular composition of the arterial wall, the effects of various interventions--cell lysis, autoclaving, and NaOH digestion--were investigated. Elastin was found to be the major determinant of ionic distribution coefficients, to possess a slight positive charge under physiological conditions, and to display a high affinity for Ca++. The distribution coefficients did not conform to the predictions of the Donnan theory of ionic equilibrium and the degree of nonideality, as measured by the fixed charge density and the ion selectivity coefficients, varied with ionic strength. Data are also presented on the distribution of neutral solutes of different molecular weights in the various arterial preparation, in order to provide a basis for comparison of the behaviour of charged solutes.

Animals↗

PubMed1988

Some factors influencing the interactions of plasma lipoproteins with arterial elastin.

Elastin is a major component of the artery wall and, because of their involvement in atherosclerosis, the interaction of lipoproteins with elastin may be of considerable importance. Previous studies of the interactions between elastin and lipoproteins have been carried out in idealised systems which do not retain the structure of the elastin. In this study we have measured the uptake of both low density lipoprotein (LDL) and high density lipoprotein (HDL) by arterial preparations and have tried to assess the importance of the different steps of preparation on the results. By comparing elastin from different sources and different degrees of extraction and delipidation we have tried to make some inferences about the nature of the interaction between elastin and lipoproteins in the hope that we can better understand the importance of this interaction in vivo.

Animals↗

PubMed1985

Reversible and irreversible interactions between elastin and plasma lipoproteins.

The interactions between radiolabeled, human plasma lipoproteins and elastin derived from bovine ligamentum nuchae were investigated using a washout technique. The interaction was characterised by Ki, a coefficient of irreversible binding, and Kr, the reversible partition coefficient. For both low-density lipoproteins (LDL) and high-density lipoproteins (HDL) the Ki values decreased as total lipoprotein concentration increased, suggesting that the binding is saturable, and were similar in magnitude to those measured by other workers using elastin derived from the human aorta. For both LDL and HDL the Kr values were independent of lipoprotein concentration in the range 0.1 microgram/ml-1.5 micrograms/ml. At a total protein concentration of 1.5 mg/ml in the incubation medium, the reversible interactions were comparable in magnitude to the irreversible.

Animals↗

PubMed1978

Herpes gestationis: studies on the binding characteristics, activity and pathogenetic significance of the complement-fixing factor.

The sera of seven out of eight patients with Herpes gestationis contained a factor which fixed C3 but not detectable amounts of immunoglobulin (Ig) on the basement membrane zone (BMZ) of normal human skin. Using C2-deficient human serum and C4-deficient guinea-pig serum, fixation was shown to be dependent upon activation of the classical pathway, and chromatography and immunoabsorption studies indicated the H. gestationis factor to be an IgG immunoglobulin. In all seven sera the H. gestationis factor bound to, and could be eluted from, the eluate of staphylococcal protein A. Although the H. gestationis factor failed to block staining of human sera by a FITC-conjugated antibody prepared from bullous pemphigoid (BP) serum, complement fixation by five out of seven sera of patients with H. gestationis was blocked using F(ab')2 of IgG prepared from pooled BP serum. In a single patient rapid resolution of lesions followed plasma exchange on two separate occasions, indicating the pathogenetic importance of humoral factors in this disease.

Basement Membrane↗