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Biomedical subjects

K Arnold

Publications and source records attributed to K Arnold.

At least 145 records · Page 8Linked to original sources
PubMed1991

Partition of serum lipoproteins in a polyethylene glycol/dextran two-phase system.

Aqueous two-phase systems containing polyethylene glycol (PEG) and dextran as phase forming polymers were used for the partition of unmodified and hypochlorite modified lipoproteins. Low density lipoprotein (LDL) was separated from high density lipoprotein (HDL) by sequential ultracentrifugation from human plasma. In agreement with the higher electrophoretic mobility, high density lipoprotein shows a higher value of the partition coefficient in contrast to low density lipoprotein. An increase in the concentration of chloride ions reduces the enrichment of lipoprotein in the top phase and favours the accumulation of aggregated material at the interface. The partition coefficient strongly depends on the age of the lipoprotein sample. Differences in the value of the partition coefficient could be obtained for the lipoprotein fractions HDL-2 and HDL-3. Hypochlorite modified LDL shows higher values of the partition coefficient due to the higher negative charge of the modified lipoprotein particle.

Chemical Phenomena↗
PubMed1991

Modification of low density lipoproteins by sodium hypochlorite.

Human low density lipoproteins (LDL) were incubated with increasing amounts of sodium hypochlorite. A decrease of the number of free amino groups on the LDL surface starts only upon addition of 30-40 moles NaOCl per mole apoB, whereas all detectable SH groups are oxidized after addition of nearly 17-20 moles NaOCl. All hypochlorite-modified LDL samples have a higher electronegative surface charge compared with native LDL as revealed by agarose gel electrophoresis and partition of LDL in an aqueous polyethylene glycol/dextran two-phase system. The more NaOCl is used to alter LDL, the higher is the electrical surface charge. Changes in surface charge are found already at low NaOCl concentrations where no decrease of amino groups is detected. It is assumed that changes in surface charge are caused by the formation of monochloramines and especially at low degrees of modification by a further unknown contribution. An effect on the primary structure of apoB or peroxidation-like changes in NaOCl-altered LDL could not be found under our experimental conditions. The results are discussed with respect to such modifications under in vivo conditions by hypochlorous acid generated in stimulated phagocytosing cells.

Dextrans↗
PubMed1991

Aggregation of human plasma high density lipoproteins induced by poly(ethylene glycol).

The influence of different surface charge densities (induced by varying pH, addition of positively charged amphiphilic molecules and chemical modification) of high density lipoproteins (isolated by ultracentrifugation) on poly(ethylene glycol) induced aggregation was studied. The effects of different molecular masses of PEG, HDL concentration and the presence of other serum proteins on the PEG mediated aggregation were investigated. The PEG concentration necessary for HDL aggregation is inversely proportional to the used HDL concentration and its molecular weight, and is directly proportional to the presence of other proteins and the magnitude of the negative surface charge density of HDL. The results are in accordance with the predictions of the volume exclusion theory taking into account the influence of repulsive electrostatic forces on the interaction of HDL particles.

Chemical Precipitation↗
PubMed1990

Surface dielectric constant, surface hydrophobicity and membrane fusion.

Membrane fusion induced by ions and its associated membrane property, surface dielectric constant, were studied with the use of acidic and neutral phospholipid vesicles. The fusion of vesicles was monitored by utilizing two fluorescence fusion assays: fluorescence content mixing method and fluorescence labelled membrane component dilution method. For the surface dielectric constant measurements, a fluorescence method was used which detected the environmental effect on the membrane surface upon the addition of various fusogenic cations. Also, the effects of poly-(ethylene glycol) on both fusion and surface dielectric properties were examined. It was found that the extent of fusion correlated well with the degree of lowering in the dielectric constant of the surface membrane, which corresponds to the increase in hydrophobicity of the membrane surface. This agrees with the previously obtained experimental results that the increase in interfacial tension of the membrane, which also corresponds to the increase in surface hydrophobicity, correlates with the extent of membrane fusion.

Calcium↗
PubMed1990

[Biophysical research on condylar temporomandibular joint growth].

On the basis of results obtained from the study of mechanically induced potentials and pulsed 1H-NMR investigations of the condylar cartilage of the TMJ in vitro, the hypothesis is advocated that the internal regulation of condylar growth takes place with the aid of bioelectric signals. Reference in made to the importance of the studies for a future noninvasive diagnosis of condylar growth in the course of functional orthopedic treatment, using "dynamic" magnetic resonance imaging.

Animals↗
PubMed1990

Depletion flocculation and depletion stabilization of erythrocytes.

At dextran (Mw approximately 500,000) concentrations from 2 to approximately 10%, suspensions of normal human erythrocytes flocculate in small convex agglutinates. At dextran concentrations greater than 10%, the erythrocytes resegregate in a stable monodisperse suspension. At all these dextran concentrations, the erythrocytes are coated with considerable amounts of dextran. It can be argued that at dextran concentrations from 2 to 10%, as well as at dextran concentrations greater than 10%, there is a thin layer, which is depleted of dextran, between the dextran layer adsorbed onto the erythrocytes and the bulk dextran solution. It can also be shown that there is a repulsive interaction between the two layers of dextran: one adsorbed and one free. When the adsorbed dextran layer is the most concentrated, stability must ensue, and when the dextran in free solution is the most concentrated, flocculation should occur. Below 7% dextran, the concentration of free dextran is higher than the adsorbed concentration; above 10% dextran that situation is reversed. These data correlate well with the depletion flocculation predicted for the lower concentration and the depletion stabilization predicted for the higher dextran concentration.

Biophysical Phenomena↗
PubMed1990

Exclusion of poly(ethylene glycol) from liposome surfaces.

The electrophoretic mobility of vesicles is measured for concentrations of poly(ethylene glycol) from 0 wt.% to 10 wt.%. Mixtures of phosphatidylcholines and phosphatidic acid are used. The zeta potential calculated from the electrophoretic mobility and the viscosity of the suspension becomes more negative for all vesicles studied. Binding of poly(ethylene glycol) to the phospholipid surface by addition of the poly(oxyethylene)-containing surfactant C12E8 has the opposite effect and a decrease of the zeta potential is observed. Independent measurements of the surface potential of the vesicles in the presence of PEG by use of a positively charged spin probe and ESR spectroscopy and a fluorescent pH indicator and fluorescence spectroscopy show that actually the surface potential is not changed. A theory of the electrophoretic behaviour of vesicles in the presence of PEG is given which explains the contradiction between the two methods. It is assumed that the polymer is excluded from the vesicle surface (depletion layer) and that the viscosity near the surface is lower than the viscosity in the bulk phase. The thickness of the depletion layer is calculated from the experiments. The decrease of the zeta potential in the presence of poly(oxyethylene) chains linked to the vesicle surface results from the friction increase.

Calcium↗
PubMed1990

Microelectrophoresis studies of the binding of glycosaminoglycans to phosphatidylcholine liposomes.

The binding of the glycosaminoglycans (GAG) chondroitin sulfate and heparin and the homologous molecule dextran sulfate to multilamellar dimyristoyl phosphatidylcholine (DMPC), dilaureyl phosphatidylcholine (DLPC) and egg lecithin liposomes was investigated by microelectrophoresis measurements. Drastic changes of the zeta potential of the liposomes to negative values indicate the binding of the highly anionic macromolecules. Binding depends strongly on Ca2+ and NaCl concentrations in the medium and does not occur in the absence of Ca2+. The adsorption is saturated at concentrations of about 0.1 mg/ml chondroitin sulfate and heparin and 0.01 mg/ml dextran sulfate. In the gel state of the phospholipid bilayer more GAG can associate with the surface compared to the fluid state.

Calcium↗
PubMed1990

Interaction of dextran sulfate with phospholipid surfaces and liposome aggregation and fusion.

The binding of dextran sulfate to phospholipid liposomes was investigated by microelectrophoresis experiments. The polyanion binds to neutral phospholipid liposomes (DMPC and PE) only in the presence of Ca2+. If positively charged stearylamine is incorporated in the vesicles dextran sulfate is bound without Ca2+. Negatively charged phospholipids as PS do not bind dextran sulfate, even in the presence of millimolar concentrations of Ca2+. The adsorption of dextran sulfate results in an aggregation of vesicles due to a bridging mechanism. In all cases the aggregation is followed by a disaggregation toward higher dextran sulfate concentrations. The disaggregation process starts at polymer concentrations smaller than the concentration of the onset of saturation of the adsorption. By use of the probe dilution method a fusion of small DMPC and DMPC/PE vesicles in the presence of Ca2+ and dextran sulfate was found.

Calcium↗
PubMed1990

Pharmacokinetics of the combination pyrimethamine with sulfadoxine and mefloquine (FANSIMEF) in Chinese volunteers and the relative bioavailability of a lacquered tablet.

The oral single-dose pharmacokinetics and bioavailability of mefloquine (M) in combination with pyrimethamine (P) and sulfadoxine (S) from a single non-lacquered tablet (NL; M 250 mg, P 25 mg, S 500 mg) and two lacquered tablets (L; M 125 mg, P 12.5 mg, S 250 mg) were investigated in 6 healthy Chinese volunteers. The plasma concentrations of P and S were measured by high-performance liquid chromatography with UV detector over 11 days and the plasma concentrations of M were measured by gas chromatography with electron capture for 63 days. The pharmacokinetic evaluation of each of the three components was based on the assumption of an open linear one-compartment model. The model-independent pharmacokinetic parameters such as elimination half-life and total clearance of P and S in the present study were not appreciably different from those reported previously. The pharmacokinetic parameters of elimination half-life, total clearance and apparent volume of distribution of M were 11 days, 45.8 ml/h.kg, and 14.8 l/kg, respectively. Compared to previously published data on M in Thai patients, Caucasian, Brazilian and African subjects, it was found that the elimination half-life in Chinese subjects was similar to that in Thai patients, but different from Caucasian, Brazilian and African subjects. There were significant differences in total clearance and volume of distribution among Chinese subjects and Thai patients. The differences in pharmacokinetic behaviour of M between subject groups needs to be examined further. The relative bioavailability of P, S, and M in the lacquered and non-lacquered tablet formulations in the 6 subjects studied were not significantly different with values (mean +/- SD) of 0.98 +/- 0.06, 1.28 +/- 0.20 and 1.02 +/- 0.17, respectively.

Administration, Oral↗
PubMed1990

Writing and using standards of nursing care.

This paper outlines some of the background to developments in setting nursing standards in the UK. Many nurses are busily engaged in this activity, and this paper offers a case study of the experience of standard setting in one unit. The Care of the Elderly Unit consists of 162 beds and a 50-place day hospital. Four wards accept acutely ill patients of both sexes, and a further five offer a mixture of rehabilitation and respite care. The buildings are a mixture of old workhouse-type wards and modern purpose-built facilities. A total of 170 nurses are employed in the unit which includes a team of clinical specialists and a senior nurse manager with overall responsibility for the nursing services. Staff at all levels on this team were involved in standard setting. The process of standard setting was an accumulation of eight years' work, with a more intense phase of activity in the last year. A variety of tools have been designed to test out the achievement of the standards.

Aged↗
PubMed1990

On the action of hypochlorite on human serum albumin.

The luminol-enhanced chemiluminescence of zymosan-stimulated polymorphonuclear leukocytes is continuously diminished in the presence of increasing amounts of human serum albumin (from 1 to 30 mg/ml). HSA competes with luminol for hypochlorite as shown by adding sodium hypochlorite to luminol solutions containing HSA. Titration of HSA with NaOCl affects firstly the sulfhydryl and probably the thioether groups and then the amino groups. Coincubation of zymosan-stimulated polymorphonuclear leukocytes and HSA at a ratio corresponding to normal values of healthy men causes a continuous oxidation of sulphur containing functional groups in HSA.

Fluorescence↗
PubMed1990

Influence of dextran sulfate on the fusion of Sendai virus with liposomes.

Liposomes made from phosphatidylserine and labeled with the fluorescence probe pyrene-phosphatidylcholine were used for studies of the influence of dextran sulfate on the fusion process. The fusion is monitored by the increase of the fluorescence signal due to the dilution of the fluorescence probes as a result of the fusion of liposomes with the virus. Addition of dextran sulfate inhibits the fusion process. Binding of the sulfate groups of the polymer to aminogroups on the virus proteins is considered as the reason for the inhibiting effect of this polymer on fusion.

Dextran Sulfate↗