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Biomedical subjects

R Karlsson

Publications and source records attributed to R Karlsson.

At least 19 recordsLinked to original sources
PubMed2005

Coordinated care planning for elderly patients using videoconferencing.

We studied the transfer of information during coordinated care planning between a university hospital and a local health care centre/social welfare department about 35 km away. During a seven-month study period, 10 sessions were conducted by videoconferencing and seven sessions were conducted by face-to-face conferencing. Videoconferencing reduced the time required for each coordinated care-planning session from an average of 60 to 45 min. There was also an increase in the number of participating professional categories. Travel time for the staff in the face-to-face group was 60-180 min each. Use of a care-planning report during the sessions resulted in improved quality of documentation, which contributed to better care following discharge. The technical problems that occurred did not detract from the beneficial experience of participating. Interviews with next of kin showed that they had been able to influence the content of the care during the care-planning sessions. Videoconferencing proved useful in coordinated care planning. It resulted in time saved due to reduced travel time, participation by more staff categories and an enhancement of the documentation quality.

Aged↗
PubMed2003

Application of single-particle laser desorption/ionization time-of-flight mass spectrometry for detection of polycyclic aromatic hydrocarbons from soot particles originating from an industrial combustion process.

Combustion-related soot particles were sampled in situ from the stoker system of a 0.5 MW incineration pilot plant (feeding material was wood) at two different heights over the feed bed in the third air supply zone. The collected particles were re-aerosolized by a powder-dispersing unit and analyzed by a single-particle laser desorption/ionization (LDI) time-of-flight mass spectrometer (aerosol-time-of-flight mass spectrometry, ATOFMS). The ATOFMS instrument characterizes particles according to their aerodynamic size (laser velocimetry) and chemical composition (LDI mass spectrometry). Chemical species from the particles are laser desorbed/ionized by 266 nm Nd:YAG laser pulses. ATOFMS results on individual 'real world' particles in general give information on the bulk inorganic composition. Organic compounds, which are of much lower concentrations, commonly are not detectable. However, recent off-line laser microprobe mass spectrometric (LMMS) experiments on bulk soot aerosol samples have emphasized that organic compounds can be desorbed and ionized without fragmentation in LDI experiments from black carbonaceous matrices. This paper reports the successful transfer of the off-line results to on-line analysis of airborne soot particles by ATOFMS. The detection of polycyclic aromatic hydrocarbons from soot particles is addressed in detail. The results are interpreted in the context of the recent LMMS results. Furthermore, their relevance with respect to possible applications in on-line monitoring of combustion processes is discussed.

Air Pollutants↗
PubMed2002

Diurnal rhythm and effects of oral contraceptives on serum dehydroepiandrosterone sulfate (DHEAS) are related to alterations in serum albumin rather than to changes in adrenocortical steroid secretion.

Dehydroepiandrosterone sulfate (DHEAS), which is of almost exclusive adrenal origin, is important for the androgen status in women and prepubertal children, and DHEAS assays are used in the investigation of hyperandrogenism. There are conflicting reports concerning a diurnal variation in serum DHEAS. Although of adrenocortical origin, serum DHEAS levels are decreased by oral contraceptives (OCs). DHEAS is strongly bound to serum albumin and has a very low metabolic clearance rate. The present study was performed in order to investigate whether a diurnal variation in serum DHEAS exists and, if so, whether this diurnal variation and the decreased DHEAS levels following OC use are related to alterations in adrenocortical steroids or to changes in serum albumin. Serum concentrations of DHEAS, dehydroepiandrosterone (DHEA), cortisol and albumin were determined in blood samples taken every half hour over a 24-h period in 10 healthy women before and during use of combined OCs. Significant and frequently synchronous diurnal variations in serum DHEAS and albumin were found before as well as during OC use. These variations were not synchronous with the diurnal variation in DHEA. OCs significantly decreased serum DHEAS and albumin levels. A multiple regression analysis showed changes in albumin to be the most decisive factor for the diurnal variation as and for OC-induced changes in DHEAS. Changes in serum DHEAS during the day and following OC use are related to alterations in its main binding protein, serum albumin, rather than to changes in adrenocortical steroid secretion.

Adult↗
PubMed2001

Determination of interaction kinetic constants for HIV-1 protease inhibitors using optical biosensor technology.

The interaction between HIV-1 protease and inhibitors has been studied with optical biosensor technology. Optimized experimental procedures and mathematical analysis permitted determination of association and dissociation rate constants. A sensor surface with native enzyme was unstable and exhibited a drift that was influenced by the binding of inhibitor. This was hypothesized to be due to a specific mechanism involving autoproteolysis and/or dimer dissociation. The use of a mutant predicted to be less susceptible to autoproteolysis (Q7K) than wild-type enzyme resulted in a minor effect on surface stability, while a completely stable surface was obtained by treatment of the immobilized enzyme with N-ethyl-N'-(dimethylaminopropyl)-carbodiimide and N-hydroxysuccinimide; the most stable surface was achieved by chemically modifying the Q7K enzyme. The stabilized surface was enzymatically active and the interaction with inhibitors was similar to that for native enzyme. Several of the inhibitors had very high association rates, and estimation of kinetic constants was therefore performed with a binding equation accounting for limited mass transport. Of the clinical inhibitors studied, saquinavir had the highest affinity for the enzyme, a result of the lowest dissociation rate. Although the dissociation rate for ritonavir was sixfold faster, the affinity was only twofold lower than that for saquinavir since the association rate was threefold faster. Nelfinavir and indinavir exhibited lower affinities relative to the other inhibitors, a consequence of a slower association for nelfinavir and a relatively fast dissociation for indinavir. These results show that biosensor-based interaction studies can resolve affinity into association and dissociation rates, and that these are characteristic parameters for the interaction between enzymes and inhibitors.

Amino Acid Substitution↗
PubMed2000

Covalent binding of ATPgammaS to the nucleotide-binding site in S14C-actin.

We have recently reported on the characterization of beta-actin carrying the mutation S14C in one of the phosphate-binding loops. The present paper describes the attachment of the adenosine 5'-[gamma-thio]-triphosphate (ATPgammaS) to actin containing this mutation. Treatment of S14C-actin with ATPgammaS blocked further nucleotide exchange and raised the thermal stability of the protein, suggesting the formation of a covalent bond between the sulfhydryl on the terminal phosphate of ATPgammaS and cysteine-14 of the mutant actin. The affinity of the derivatized G-actin for DNase I as compared to wild-type ATP-actin was lowered to a similar extent as that of ADP.AlF(4)-actin. The derivatized actin polymerized slower than ATP-actin but faster than ADP-actin. Under these conditions the bound ATPgammaS was hydrolyzed, suggesting the formation of a state corresponding to the transient ADP.P(i)-state. ATPgammaS-actin interacted normally with profilin, whereas the interaction with actin depolymerizing factor (ADF) was disturbed, as judged on the effects of these proteins on actin polymerization.

Actins↗
PubMed2000

Biosensor analysis of the interaction between immobilized human serum albumin and drug compounds for prediction of human serum albumin binding levels.

The interactions between a set of drugs, selected on the basis of reported human serum albumin (HSA) binding levels, and immobilized HSA were investigated using surface plasmon resonance technology. Major HSA binding sites were available after immobilization. The intensity of the signal obtained from the interaction of the drug with the HSA surface was correlated with the reported HSA binding level. Drugs were classified into groups corresponding to high, medium, or low HSA binding based on the injection of the drug at 80 microM concentration. A set of 10 drugs binding to alpha(1)-acid glycoprotein (AGP) was also investigated and correlated with reported AGP binding data. The throughput of the presented assay is 100 compounds/24 h, and the sample consumption is less than 100 microL (8 nmol).

Binding Sites↗
PubMed2000

Effects of cross-linked profilin:beta/gamma-actin on the dynamics of the microfilament system in cultured cells.

There is evidence that the profilin:actin complex is the immediate precursor in the formation of actin filaments in cells. This paper describes the cell morphology and microfilament distribution after microinjection of covalently cross-linked profilin:beta/gamma-actin (PxA) in two different cell lines. Injected cells were either kept unstimulated or stimulated with platelet-derived growth factor (PDGF) before fixation and visualization of filamentous actin. After injection of low doses of PxA, the cells displayed an actin organization characterized by a clearance of diffuse fluorescence from a region immediately interior of ruffling edges and the appearance of small dots of fluorescence in the same region. At higher concentrations, PxA effectively inhibited outgrowth of lamellae and microspikes, and there was a drastic reduction of actin staining in the zone behind the advancing edge. This effect is reminiscent of the effect of cytochalasin B on fibroblasts and the growth cone of neuronal cells. As in these cases, there remained a rim of actin-dependent fluorescence on the very edge of the membrane lamella, particularly in the PxA-treated fibroblasts. The interference of PxA with the formation of surface structures was pronounced after PDGF stimulation. Here, PxA effectively eliminated the enhancement of the ruffling activity in the cell edges and on the dorsal surface of the cells. In contrast to PxA, injection of non-cross-linked profilin:beta/gamma-actin had no apparent effect on cell morphology and microfilament distribution except for an increased concentration of filamentous actin in one of the cell lines.

Actin Cytoskeleton↗
PubMed2000

Biosensor analysis of drug-target interactions: direct and competitive binding assays for investigation of interactions between thrombin and thrombin inhibitors.

The sensitivity of BIACORE technology is sufficient for detection and characterization of binding events involving low-molecular-weight compounds and their immobilized protein targets. The technology requires no labeling and provides information on the stability of the compound/target complex with a single injection of the compound. This is useful for qualifying hits obtained in a primary screen and in lead optimization. Although immobilized targets can be reused, the surface may slowly deteriorate, solvent effects can distort binding levels during injection of compounds, and some compounds may exhibit broad protein selectivity rather than target specificity. A reliable direct binding assay for compounds binding to immobilized thrombin using a combination of two reference surfaces, a dextran surface for subtraction and calibration of solvent effects and a protein surface for identification of compounds that tend to bind proteins, has been developed. Eleven compounds with known binding specificity to thrombin and 159 additional compounds were investigated. All compounds with known binding specificity were identified at 1 and 10 microM concentration. One additional compound was scored as positive. The direct binding assay compared favorably with two competitive assay formats, a surface competitive assay and a inhibitor in solution assay, that were examined in parallel.

Antithrombins↗
PubMed2000

Thermal unfolding of G-actin monitored with the DNase I-inhibition assay stabilities of actin isoforms.

Actin is one of the proteins that rely on chaperonins for proper folding. This paper shows that the thermal unfolding of G-actin, as studied by CD and ultraviolet difference spectrometry, coincides with a loss in DNase I-inhibiting activity of the protein. Thus, the DNase I inhibition assay should be useful for systematic studies of actin unfolding and refolding. Using this assay, we have investigated how the thermal stability of actin is affected by either Ca2 + or Mg2 + at the high affinity divalent cation binding site, by the concentration of excess nucleotide, and by the nucleotide in different states of phosphorylation (ATP, ADP.Pi, ADP. Vi, ADP.AlF4, ADP.BeFx, and ADP). Actin isoforms from different species were also compared, and the effect of profilin on the thermal stability of actin was studied. We conclude that the thermal unfolding of G-actin is a three-state process, in which an equilibrium exists between native actin with bound nucleotide and an intermediate free of nucleotide. Actins in the Mg-form were less stable than the Ca-forms, and the stability of the different isoforms decreased in the following order: rabbit skeletal muscle alpha-actin = bovine cytoplasmic gamma-actin > yeast actin > cytoplasmic beta-actin. The activation energies for the thermal unfolding reactions were in the range 200-290 kJ.mol- 1, depending on the bound ligands. Generally, the stability of the actin depended on the degree with which the nucleotide contributed to the connectivity between the two domains of the protein.

Actins↗
PubMed2000

Parameters characterizing electromagnetic wave polarization

In this paper, generalizations of the Stokes parameters and alternative characterizations of three-dimensional (3D) time-varying electromagnetic fields is introduced. One of these characteristics is the normal of the polarization plane, which, in many cases of interest, is parallel (or antiparallel) to the direction of propagation. Others are the two spectral density Stokes parameters which describe spectral intensity and circular polarization. The analysis is based on the spectral density tensor. This tensor is expanded in a base composed of the generators of the SU(3) symmetry group, as given by Gell-Mann and Y. Ne'eman [The Eight-fold Way (Benjamin, New York, 1964)] and the coefficients of this expansion are identified as generalized spectral density polarization parameters. The generators have the advantage that they obey the same algebra as the Pauli spin matrices, which is the base for expanding the 2D spectral density tensor with the Stokes parameters as coefficients. The polarization parameters introduced are formulated in the frequency domain, thereby further generalizing the theory to allow for wide-band electromagnetic waves in contrast to the traditional quasi-monochromatic formulation.

Journal Article↗
PubMed2000

Antenatal and early postnatal dexamethasone treatment decreases cortisol secretion in preterm infants.

Glucocorticoids are used antenatally to accelerate the maturation of fetal respiratory and cardiovascular systems when a threat of preterm delivery exists. Postnatally, they are used to prevent and treat respiratory distress syndrome. This study investigates the effects of antenatal (ACT) and early postnatal corticosteroid treatment (PCT) on serum cortisol and plasma catecholamine and adenosine 3',5'-cyclic monophosphate (cAMP) concentrations in preterm neonates. The infants in the ACT group had a significantly lower cortisol concentration than the infants in the non-ACT group on the first day of life. After birth, the infants were further divided into non-PCT and PCT groups. PCT suppressed cortisol levels significantly after 2 days, and the cortisol levels were still lower 2 days after discontinuation of PCT. No effect of PCT on plasma cAMP or catecholamine concentrations was observed. The results indicate that both ACT and a short PCT can significantly suppress basal cortisol levels in preterm infants.

Catecholamines↗
PubMed2000

Adrenocorticotropin and corticotropin-releasing hormone tests in preterm infants.

The short ACTH test is used in evaluating the hypothalamo-pituitary-adrenal axis (HPA-axis) in preterm neonates after dexamethasone treatment. This test mainly examines primary adrenal suppression but is also used as a method to test secondary adrenal insufficiency because long-term deprivation of ACTH causes atrophy of the adrenal cortex. The CRH test, on the other hand, directly examines the function of the pituitary. We tested 18 infants in the neonatal intensive care unit with both the ACTH test and the CRH test to determine which of these two tests more reliably demonstrates HPA-axis suppression. One patient had normal responses both in the ACTH test and in the CRH test when the limit of 360 nmol/L was used as a sign of proper cortisol secretion. In four cases the patients' cortisol secretion would have been regarded as normal by the low-dose ACTH test, whereas the CRH test did not show an adequate cortisol response. In conclusion, the ACTH test did not reliably indicate HPA-axis suppression after a short (<2 weeks) course of dexamethasone therapy in this study. Therefore, whether the infant is or will be under acute stress after short glucocorticoid treatment, ensuring adequate cortisol secretion with the CRH test should be considered.

Adrenal Gland Diseases↗
PubMed2000

The PI 3-kinase isoforms p110(alpha) and p110(beta) have differential roles in PDGF- and insulin-mediated signaling.

Phosphoinositide 3'-kinases constitute a family of lipid kinases implicated in signal transduction through tyrosine kinase receptors and heterotrimeric G protein-linked receptors. Phosphoinositide 3'-kinases that bind to the platelet-derived growth factor receptor are composed of two subunits: the p85 subunit acts as an adapter and couples the catalytic p110 subunit to the activated receptor. There are different isoforms of p85 as well as of p110, the individual roles of which have been elusive. Using microinjection of inhibitory antibodies specific for either p110(alpha) or p110(beta) we have investigated the involvement of the two p110 isoforms in platelet-derived growth factor- and insulin-induced actin reorganization in porcine aortic endothelial cells. We have found that antibodies against p110(alpha), but not antibodies against p110(beta), inhibit platelet-derived growth factor-stimulated actin reorganization, whereas the reverse is true for inhibition of insulin-induced actin reorganization. These data indicate that the two phosphoinositide 3'-kinase isoforms have distinct roles in signal transduction pathways induced by platelet-derived growth factor and insulin.

Actins↗
PubMed2000

Mutational analysis of arginine 177 in the nucleotide binding site of beta-actin.

Actin ADP-ribosylated at arginine 177 is unable to hydrolyze ATP, and the R177 side chain is in a position similar to that of the catalytically essential lysine 71 in heat shock cognate protein Hsc70, another member of the actin-fold family of proteins. Therefore, actin residue R177 has been implicated in the mechanism of ATP hydrolysis. This paper compares wild-type beta-actin with a mutant in which R177 has been replaced by aspartic acid. The mutant beta-actin was expressed in Saccharomyces cerevisiae and purified by DNase I-affinity chromatography. The mutant protein exhibited a reduced thermal stability and an increased nucleotide exchange rate, suggesting a weakened interdomain connection. The ATPase activity of G-actin and the ATPase activity expressed during polymerization were unaffected by the R177D replacement, showing that this residue is not involved in catalysis. In the presence of polymerizing salts, ATP hydrolysis by both wild-type Mg-beta-actin and the mutant protein preceded filament formation. With the mutant actin, the initial rate of ATP hydrolysis was as high as with wild-type actin, but polymer formation was slower, reached lower steady-state levels, and the polymers formed exhibited much lower viscosity. The critical concentration of polymerization (Acc) of the mutant actin was increased 10-fold as compared to wild-type actin. Filaments formed from the R177D mutant beta-actin bound phalloidin.

Actins↗
PubMed1999

Mutational analysis of Ser14 and Asp157 in the nucleotide-binding site of beta-actin.

This paper compares wild-type and two mutant beta-actins, one in which Ser14 was replaced by a cysteine, and a second in which both Ser14 and Asp157 were exchanged (Ser14-->Cys and Ser14-->Cys, Asp157-->Ala, respectively). Both of these residues are part of invariant sequences in the loops, which bind the ATP phosphates, in the interdomain cleft of actin. The increased nucleotide exchange rate, and the decreased thermal stability and affinity for DNase I seen with the mutant actins indicated that the mutations disturbed the interdomain coupling. Despite this, the two mutant actins retained their ATPase activity. In fact, the mutated actins expressed a significant ATPase activity even in the presence of Ca2+ ions, conditions under which actin normally has a very low ATPase activity. In the presence of Mg2+ ions, the ATPase activity of actin was decreased slightly by the mutations. The mutant actins polymerized as the wild-type protein in the presence of Mg2+ ions, but slower than the wild-type in a K+/Ca2+ milieu. Profilin affected the lag phases and elongation rates during polymerization of the mutant and wild-type actins to the same extent, whereas at steady-state, the concentration of unpolymerized mutant actin appeared to be elevated. Decoration of mutant actin filaments with myosin subfragment 1 appeared to be normal, as did their movement in the low-load motility assay system. Our results show that Ser14 and Asp157 are key residues for interdomain communication, and that hydroxyl and carboxyl groups in positions 14 and 157, respectively, are not necessary for ATP hydrolysis in actin.

Actins↗