Search PubMed⌕ Search

Biomedical subjects

C Karlsson

Publications and source records attributed to C Karlsson.

At least 55 records · Page 3Linked to original sources
PubMed1997

Structure of the O-polysaccharide from the LPS of a Hafnia alvei strain isolated from a patient with suspect yersinosis.

The carbohydrate backbone of the Hafnia alvei strain Y166/91 lipopolysaccharide (LPS) was isolated by mild acid hydrolysis followed by gel permeation chromatography and studied by NMR spectroscopy and methylation analysis. Treatment with periodate and hypoiodite gave a modified polysaccharide which was also characterised. It was concluded that the polysaccharide has the following structure with two distinct regions, which are connected. The chain length parameters m and n were not determined but the ratio m/n is approximately 2. [-->3)-beta-D-Galp-1(1-->3)-alpha-D-Galp-(1-->]m[-->3)-alpha-D-Galp-(1-- >3)- beta-D-Galf-(1-->]n From the present data it is not possible to determine whether it is the Galp-Galp chain or the Galp-Galf chain that is connected to the core. The structure found here is identical to that suggested for the O-specific polysaccharide chain of Klebsiella pneumoniae O1K2 (NCTC 5055) LPS [O. Kol, J.-M. Wieruszeski, G. Strecker, J. Montreuil, and B. Fournet, Carbohydr. Res., 217 (1991) 117-125; O. Kol, J.-M. Wieruszeski, G. Strecker, B. Fournet, R. Zalisz, and P. Smets, Carbohydr. Res., 236 (1992) 339-344].

Carbohydrate Sequence↗
PubMed1997

Obese (ob) gene defects are rare in human obesity.

Our knowledge of the role of the recently cloned ob-protein (leptin) in the regulation of body fat stores is largely derived from experiments performed in mice. Different mouse models exhibit abnormalities in ob-gene expression, with extreme overexpression in mice which lack bioactive ob-protein, have nonfunctional ob-receptors or hypothalamic lesions, and undetectable expression in mice with suggested defects in regulatory elements. The aim of this study is to examine if defects, corresponding to those in mice, exist in human obesity. Adipose tissue was obtained from 94 adult obese subjects and from six children who had developed obesity after surgery in the hypothalamic region. Total RNA was isolated and ob-gene expression was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Northern blot. The coding region of the ob-gene was sequenced in both directions in the 94 obese adults. No mutations were detected in the coding region of the ob-gene and ob-gene expression was detectable in all subjects and none of the subjects had an extreme overexpression. There was no systematic increase in ob-expression in obese children with hypothalamic disease compared to their healthy brothers and sisters. These results show that severe abnormalities involving the ob-gene, analogous to those described in mouse models, are rare in human obesity. We therefore conclude that the cloning and subsequent analysis of the ob-gene has not provided information that can, by itself, explain the genetic component in the development of human obesity.

Adipose Tissue↗
PubMed1997

5-Hydroxytryptamine contracts human uterine artery smooth muscle predominantly via 5-HT2 receptors.

Serotonergic receptors were classified in the isolated human uterine artery with intact endothelium, using agonists and antagonists for 5-hydroxytryptamine (5-HT) receptors. The efficacy for different agonists rated: alpha-methyl-5-HT (5-HT2) = 5-HT (non-selective) = 2-methyl-5-HT (5-HT3) >> sumatriptan (5-HT1), and the potency as: sumatriptan = 5-HT > 5-HT > alpha-methyl-5-HT > 2-methyl-5-HT. The contractile effects of 5-HT and alpha-methyl-5-HT were antagonized by the 5-HT2 receptor antagonist ketanserin and the non-selective antagonist methiothepin. The efficacy of sumatriptan was comparatively low. No interaction was encountered between 2-methyl-5-HT and MDL72222, suggesting an absence of 5-HT3 receptors. The results indicate that the contractile serotonergic receptor population in the human uterine artery mainly comprises 5-HT2 receptors, although a minor contribution of contractile 5-HT1 receptors cannot be excluded.

Dose-Response Relationship, Drug↗
PubMed1997

Expression of functional leptin receptors in the human ovary.

The size of body fat stores is known to influence fertility, indicating a link between adipose tissue and the reproductive system. Studies in mice have identified the adipocyte-derived hormone, leptin (Ob protein), as a possible mediator of this effect. The aim of this study was to investigate the possibility that leptin may have direct effects on the human ovary. To probe this hypothesis we first analyzed the expression of leptin receptors in the human ovary. Transcripts encoding both the long and short isoforms of the leptin receptor were present in human granulosa cells and thecal cells; however, the short isoforms were expressed at much higher levels. Immunoreactive leptin was present in follicular fluid at levels similar to those found in serum. ob gene expression, however, was undetectable in the ovary, as determined by reverse transcription-PCR, whereas it was easily detected in adipose tissue. To determine whether leptin could induce a biological response in ovarian cells, we examined the effect of leptin on estradiol production in cultured granulosa cells. Leptin (100 ng/mL) inhibited LH (0.1 ng/mL)-stimulated estradiol production. In contrast, leptin had no effect on estradiol production in the absence of LH. In conclusion, this study has demonstrated that the leptin receptor is expressed in the human ovary, that leptin is present in follicular fluid, and that leptin can induce a biological response in ovarian cells. These results suggest that leptin may have a direct effect on the human ovary.

Adult↗
PubMed1996

Dynamics of root growth in microgravity.

An experiment to study the growth of garden cress roots in microgravity is described. The experiment, denoted RANDOM, was an ESA Biorack experiment in the IML-2 flight in July 1994. In the absence of gravity, it can be anticipated that the roots would show random growth, changing their direction randomly. The hypothesis that such random growth movements occur according to random walk theory, leads to predictions as to the detailed manner in which deviations increase with time. The experiment was designed to test this random walk hypothesis. The paper concentrates on the technological aspects of studying the roots in microgravity. The development of suitable plant chambers, fitting containers developed by ESA, is described as well as the techniques used to grow the seeds between agar slices. hardware was developed to record photographically root movements between the agar slices. Photos were taken once per hour. Some plant chambers were designed to allow fixation of plant material in space. The practical solutions found using glutaraldehyde for prefixation in the Spacelab, within the restrictions given, are described. The experimental results show that the growth pattern in fact followed the prediction from the random walk approach. The average changes in the growth direction stayed constant and equal to zero during the experiment while the squared angular deviations increased proportional to time. Furthermore, plant material prefixed in orbit was permanently fixed after the flight. Light microscopy and electron microscopy pictures are shown as examples of the results achieved. The long prefixation period meant a drawback for the quality of the fixation process. However, sections suitable for study were achieved. The main goals of the RANDOM experiment were therefore achieved.

Environment, Controlled↗
PubMed1996

Escape from senescence in hybrid cell clones involves deletions of two regions located on human chromosome 1q.

Human normal cells have been shown to undergo a limited number of cell doublings, a phenomenon termed cellular senescence. Human chromosome 1 has been implicated in this process, and several lines of evidence indicate that there is a senescence-inducing gene or genes on human chromosome 1q. Our approach to analyze the senescence-inducing effect of chromosome 1 includes the use of somatic cell hybrid revertants. We show here that fusion of a hypoxanthine phosphoribosyl transferase-negative mouse cell line (A9) containing a human neo-tagged chromosome 1 with an immortal hamster cell line (10W-2) results in cell hybrids that senesce after a few population doublings. Rare revertants that had escaped senescence were obtained after one large fusion experiment. Thirty-five nonsenescent hybrids were obtained from a total of approximately 1 million hybrids, and 25 of these were subjected to further analysis. The presence of a single copy of human chromosome 1 in the revertant hybrids was confirmed by fluorescence in situ hybridization analysis using a chromosome 1-specific painting probe. No visible translocations or deletions of chromosome 1 were observed in any of the hybrids. Deletion mapping revealed that 11 (56%) of the hybrids analyzed had lost one or more markers on chromosome 1q. Two regions with deletions were detected, one of which has been shown to be implicated in the senescence-inducing effect exerted by chromosome 1 following monochromosome transfer (P. J. Vojta et al., manuscript submitted for publication). The present study suggests that two separate loci on human chromosome 1q may be of importance for the induction of senescence. Moreover, this set of nonsenescent revertants could be useful for future detailed analyses of the senescence-inducing loci.

Animals↗
PubMed1996

Bcl-2 immunoreactivity in salivary gland neoplasms is unrelated to the expression of mRNA for natural killer cell stimulatory cytokines interleukin (IL)-2 and IL-12.

Certain cytokines are involved in the generation of natural killer (NK) cells and participate in the regulation of the proto-oncogene bcl-2. We aimed to study the mRNA expression of interleukin (IL)-2, IL-4 and IL-5, the composition of the tumour infiltrating lymphocytes (TIL), and the expression of bcl-2 in 14 benign and malignant human parotid tumours. T IL were predominantly composed of T lymphocytes and NK cells. We found evidence for the homing of T cells, and for generation of NK cells in the vicinity of the tumours. mRNA for IL-2 and IL-12, were identified but IL-4 mRNA was not found. The cytokine profiles and the composition of TIL of the two tumour categories were indistinguishable, suggesting that these host-response variables do not explain the differences in biological behaviour of these particular tumours. The results support a shift towards Th 1 (T helper 1) cells and interferon-gamma production, and that IL-12 also in vivo may play an important role in the regulatory interaction between innate resistance and adaptive immunity in tumour diseases. Most infiltrating lymphocytes showed strong expression of bcl-2; an interesting observation with regard to lymphocytic apoptosis in neoplastic diseases. The immunoreactivity for the bcl-2 protein varied considerably between and within tumours, and almost all benign tumours showed strong bcl-2 positively whereas several of the malignant tumours showed weak or absent staining. The variable expression of bcl-2 protein suggests a different susceptibility of tumour cells to apoptosis. The results also indicate that bcl-2 cannot pla a major role as protective agent in the specific apoptotic pathway induced by NK cells.

Humans↗
PubMed1996

Exposure of blood to biomaterial surfaces liberates substances that activate polymorphonuclear granulocytes.

Human whole blood, anticoagulated or not, was exposed to hydrophilic glass surfaces or methylated hydrophobic glass surfaces under saline cover. Platelet-poor plasma or serum was prepared after 10 minutes of exposure, measured in respect to complement activation, and transferred to a suspension of granulocytes, which acted as bioprobes. The granulocytes were prepared from blood, anticoagulated with ethylenediaminetetraacetic acid, and evaluated regarding intracellular Ca2+ concentration (Calcium Green-1 fluorescence), integrin expression (CD-11b immunohistochemistry), respiratory burst (chemiluminescence), and priming (increase in N-formyl-methionyl-leucyl-phenylalanine-induced respiratory burst). The results indicate that humoral factors formed during the surface exposure of blood were able to activate the probe granulocytes. The exposure to hydrophilic surfaces led to a calcium transient three times the magnitude of that of hydrophobic surfaces. This response could be blocked by the presence of heparin during the blood-surface exposure but was not affected by the addition of heparin to the probe granulocytes. Hirudin, a specific thrombin blocker, had no effect. The exposure to hydrophobic surfaces led to complement activation in serum that induced priming and respiratory burst of the probe granulocytes. In conclusion, the study provides evidence that hydrophilic-hydrophobic surface treatment significantly affects the immediate inflammatory response of a blood-biomaterial interaction that is moderated by the presence of heparin.

Antithrombins↗
PubMed1996

Random root movements in weightlessness.

The dynamics of root growth was studied in weightlessness. In the absence of the gravitropic reference direction during weightlessness, root movements could be controlled by spontaneous growth processes, without any corrective growth induced by the gravitropic system. If truly random of nature, the bending behavior should follow so-called 'random walk' mathematics during weightlessness. Predictions from this hypothesis were critically tested. In a Spacelab ESA-experiment, denoted RANDOM and carried out during the IML-2 Shuttle flight in July 1994, the growth of garden cress (Lepidium sativum) roots was followed by time lapse photography at 1-h intervals. The growth pattern was recorded for about 20 h. Root growth was significantly smaller in weightlessness as compared to gravity (control) conditions. It was found that the roots performed spontaneous movements in weightlessness. The average direction of deviation of the plants consistently stayed equal to zero, despite these spontaneous movements. The average squared deviation increased linearly with time as predicted theoretically (but only for 8-10 h). Autocorrelation calculations showed that bendings of the roots, as determined from the 1-h photographs, were uncorrelated after about a 2-h interval. It is concluded that random processes play an important role in root growth. Predictions from a random walk hypothesis as to the growth dynamics could explain parts of the growth patterns recorded. This test of the hypothesis required microgravity conditions as provided for in a space experiment.

Brassicaceae↗
PubMed1995

Structural organization of the human sorbitol dehydrogenase gene (SORD).

The primary structure of human sorbitol dehydrogenase (SORD) was determined by cDNA and genomic cloning. The nucleotide sequence of the mRNA covers 2471 bp including an open reading frame that yields a protein of 356 amino acid residues. The gene structure of SORD spans approximately 30 kb divided into 9 exons and 8 introns. The gene was localized to chromosome 15q21.1 by in situ hybridization. Two transcription initiation sites were detected. Three Sp1 sites and a repetitive sequence (CAAA)5 were observed in the 5' noncoding region; no classical TATAA or CCAAT elements were found. The related alcohol dehydrogenases and zeta-crystallin have the same gene organization split by 8 introns, but no splice points coincide between SORD and these gene types. The deduced amino acid sequence of the SORD structure differs at a few positions from the directly determined protein sequence, suggesting allelic forms of the enzyme. High levels of SORD transcripts were observed in lens and kidney, as judged from Northern blot analysis.

Amino Acid Sequence↗
PubMed1995

Gravitropic responses of the Avena coleoptile in space and on clinostats. II. Is reciprocity valid?

Experiments were undertaken to determine if the reciprocity rule is valid for gravitropic responses of oat coleoptiles in the acceleration region below 1 g. The rule predicts that the gravitropic response should be proportional to the product of the applied acceleration and the stimulation time. Seedlings were cultivated on 1 g centrifuges and transferred to test centrifuges to apply a transverse g-stimulation. Since responses occurred in microgravity, the uncertainties about the validity of clinostat simulation of weightlessness was avoided. Plants at two stages of coleoptile development were tested. Plant responses were obtained using time-lapse video recordings that were analyzed after the flight. Stimulus intensities and durations were varied and ranged from 0.1 to 1.0 g and from 2 to 130 min, respectively. For threshold g-doses the reciprocity rule was obeyed. The threshold dose was of the order of 55 g s and 120 g s, respectively, for two groups of plants investigated. Reciprocity was studied also at bending responses which are from just above the detectable level to about 10 degrees. The validity of the rule could not be confirmed for higher g-doses, chiefly because the data were more variable. It was investigated whether the uniformity of the overall response data increased when the gravitropic dose was defined as (gm x t) with m-values different from unity. This was not the case and the reciprocity concept is, therefore, valid also in the hypogravity region. The concept of gravitropic dose, the product of the transverse acceleration and the stimulation time, is also well-defined in the acceleration region studied. With the same hardware, tests were done on earth where responses occurred on clinostats. The results did not contradict the reciprocity rule but scatter in the data was large.

Acceleration↗
PubMed1994

Features of structural zinc in mammalian alcohol dehydrogenase. Site-directed mutagenesis of the zinc ligands.

All four cysteine ligands to the structural zinc atom of human class-I and class-III alcohol dehydrogenase have been exchanged by site-directed mutagenesis in order to study the importance of the metal in the mammalian enzymes. The cysteine residues were replaced with Ala and Ser, residues that are not able to ligand zinc. All mutations resulted in inactive, unstable enzymes, in contrast to the non-mutated human alcohol dehydrogenases that are easily isolated. Northern-blot analysis revealed the presence of the expected mRNAs from expression plasmids constructed with the different mutated and non-mutated alcohol dehydrogenases, and Western-blot analysis gave faint signals for the mutated recombinant proteins from crude extracts. This verifies that the plasmid constructs are correct, but that the translated, mutated proteins lacking the zinc-stabilized local fold, are subject to rapid degradation. Hence, the results directly illustrate the importance of the structural zinc atom in mammalian alcohol dehydrogenase and confirm it as a component with 'structural' properties. The results are compatible with those from sensitivities to proteases and from the structures of other proteins within the super-family, indicating that the structural role of the zinc atom may involve conservation of interfaces regulating the enzyme quaternary structure.

Alcohol Dehydrogenase↗
PubMed1994

Age related induction of platelet-derived growth factor A-chain mRNA in normal human fibroblasts.

We have previously found that stimulation of normal neonatal fibroblasts with PDGF or EGF leads to a transient induction of PDGF A-chain mRNA and the synthesis of PDGF-AA proteins. This finding may imply the existence of an autocrine feedback mechanism to amplify the mitogenic signal under certain conditions. We have now studied the PDGF-BB mediated PDGF A-chain induction in a set of fibroblasts from young and old donors to clarify if the levels of induction are correlated to the donor age and the replicative capacity of the cells. The PDGF A-chain induction was found to be reduced in cells from old donors compared with cells from embryonic and neonatal donors. The different cell strains were also characterized further with respect to PDGF receptor expression and PDGF binding properties. PDGF beta-receptors were found to be enhanced in old donor cell strains, whereas the PDGF alpha-receptors showed more variability in expression between the strains. The PDGF A-chain mRNA induction was also decreased or absent in late passage human fibroblasts (senescent cells) when compared with early passage cells. These data suggest that the PDGF A-chain mRNA induction is regulated by an age related mechanism in human fibroblasts.

Aged↗
PubMed1993

Zinc coordination in mammalian sorbitol dehydrogenase. Replacement of putative zinc ligands by site-directed mutagenesis.

Rat sorbitol dehydrogenase was expressed in Escherichia coli and purified to homogeneity, resulting in a protein with a specific activity of 4.7 U/mg, close to that of the enzyme isolated from mammalian liver. A Glu residue has been postulated to replace the Cys of alcohol dehydrogenase as a ligand to the active-site zinc atom of sorbitol dehydrogenase. This Glu (position 155 in the rat enzyme) was mutated both to Cys, in order to mimic the alcohol dehydrogenase relationships, and to Ala, as a control. A third mutation, Cys164 to Ala, was also performed since Cys has also been considered as a possible zinc ligand. With Ala at position 155, an inactive enzyme was obtained, showing that correct active-site relationships have been destroyed. With Cys at position 155, the enzyme is still partly active, but rapidly looses activity unless stabilized by the addition of ZnSO4. The catalytic efficiency in the oxidation of sorbitol is 120-fold less than that of the native form, and reduction of fructose is lost completely. In contrast, the activity of the Cys164Ala mutant is comparable with that of the native enzyme and, in fact, even increased in the oxidation of sorbitol. Combined, the results strongly suggest that Glu155 is a ligand to the active-site zinc atom. Zinc analysis of the different variants of sorbitol dehydrogenase establishes that all contain one atom of zinc/subunit, also when the catalytic function is lost. Apparently, zinc remains coordinated even after replacement with an amino acid residue (Ala) unable to ligand metal atoms.

Animals↗
PubMed1993

Distribution of alcohol and sorbitol dehydrogenases. Assessment of mRNA species in mammalian tissues.

The tissue distribution of mRNA of alcohol dehydrogenases of classes I, II and III, and sorbitol dehydrogenase, was studied. mRNA from 19 different rat tissues was purified and analyzed by Northern blots, utilizing cDNA probes specific for the four dehydrogenases. Class-I alcohol-dehydrogenase mRNA was shown to be of widespread occurrence, detectable in all tissues including brain, but with pronounced differences in amounts. Hybridization revealed the pattern of occurrence of class-II alcohol-dehydrogenase mRNA to be unique, with transcripts only in the liver, duodenum, kidney, stomach, spleen and testis. Abundant levels of class-III alcohol-dehydrogenase (glutathione-dependent formaldehyde dehydrogenase) mRNA were present in all tissues analyzed, reflecting the general need for scavenging of formaldehyde in physiological cytoprotection. Sorbitol dehydrogenase mRNA was detected in all tissues except small intestine, in agreement with sorbitol resorbtion by passive diffusion in this tissue. In addition, evidence for a sex-specific expression, in the liver, of class-II alcohol dehydrogenase was obtained.

Alcohol Dehydrogenase↗
PubMed1993

Density-dependent inhibitory effect of transforming growth factor-beta 1 on human fibroblasts involves the down-regulation of platelet-derived growth factor alpha-receptors.

We have previously found that transforming growth factor-beta 1 (TGF-beta 1) inhibits the mitogenic activity of platelet-derived growth factor (PDGF) in cultures of human neonatal fibroblasts in a density-dependent fashion. In the present investigation we determined the effect of TGF-beta 1 on the PDGF alpha-receptor, which binds all PDGF isoforms, as well as on the beta-receptor, which binds only PDGF-BB with high affinity. We found that the inhibitory effect of TGF-beta 1 on PDGF-AA-induced mitogenesis was density-dependent; when dense cell cultures were preincubated with TGF-beta 1, there was an complete inhibition of 3H-thymidine incorporation, whereas the effect was less in sparse cultures. A similar density-dependent effect of TGF-beta 1 was seen in PDGF-BB treated cells, although less pronounced. The binding of 125I-labeled PDGF-AA and PDGF-BB to the alpha-receptor was significantly reduced after treatment with TGF-beta 1 in dense cultures, whereas the sparse cultures were less affected. A decrease of alpha-receptor mRNA was also seen. The levels of beta-receptor protein and mRNA were unaffected. We conclude that the growth inhibitory effect of TGF-beta 1 is cell density-dependent and involves down-regulation of PDGF alpha-receptors.

Cell Count↗