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Biomedical subjects

D Sommer

Publications and source records attributed to D Sommer.

At least 19 recordsLinked to original sources
PubMed2005

[Osteoblast reaction on SLA and microgrooved implant surfaces].

The osseointegration process of dental implants depends on the tissue reaction at the tissue-implant interface. Osteoblasts are the main cells responsible for the regulation of osteoinduction. The manner and kinetics of the tissue reaction crucially depend on the interaction between osteoblasts and the morphology of the implant surface. The aim of this study was to investigate osteoblast behaviour on different implant surfaces (smooth, microgrooved, SLA) under standardized conditions. For this in vitro investigation we used primary bovine osteoblasts. Attachment kinetics, proliferation rate and synthesis of bone-associated proteins were used as parameters for cell reaction. The results demonstrate that both attachment and adhesion strength of the primary cell surface interaction was higher on the microgrooved surfaces than on SLA surfaces. The proliferation rate of cells and the synthesis of bone-specific proteins were higher on microgrooved surfaces in contrast to SLA surfaces. Ultrastructural analysis revealed phenotypic osteoblast-like cells on smooth and microgrooved surfaces, whereas cells on SLA surfaces showed a more fibroblastic appearance. This study demonstrates that the morphology of the implant surface determined the subsequent osteoblast reaction. An optimal cell reaction was found at surfaces which are smooth in the microenvironment of osteoblasts.

Animals↗
PubMed2005

A quantitative analysis of anaesthetist-patient communication during the pre-operative visit.

Previous communication research in general medical practice has shown that effective communication enhances patient compliance, satisfaction and medical outcome. It is expected that communication is equally important in anaesthesia, since patients often suffer from anxiety and lack of knowledge about anaesthetic procedures. However, little is known about the nature of communication during routine anaesthetic visits. The present study of 57 authentic anaesthetic visits provides the first results on the structure and content of communication in the pre-operative setting using the Roter Interaction Analysis System (RIAS). Patient-centred communication behaviours of anaesthetists and the extent of patient involvement were particularly investigated. From the 57 pre-operative visits, 18 267 utterances were coded. The mean (SD) [range] duration of the visit was 16.1 (7.8) [3.7-42.7] min. Anaesthetists provided 169 (68) and patients 153 (82) utterances per visit (53.5% vs. 46.5%). Physician and patient gender had no impact on the distribution of utterances and the duration of the visit. Conversation mainly focussed on biomedical issues with little psychosocial discussion (< 0.1% of all anaesthetist utterances). However, anaesthetists quite frequently used emotional comments toward patients (7%) and involved them in the conversation. The use of facilitators, open questions and emotional statements by the anaesthetist correlated with high patient involvement. The amount of patient participation in anaesthetic decisions was assessed with the Observing Patient Involvement Scale (OPTION). Compared with general practitioners, anaesthetists offered more opportunities to discuss treatment options (mean (SD) OPTION score 26.8 (16.8) vs. 16.8 (7.7)).

Adult↗
PubMed2000

Advances in the management of major airway collapse: the use of airway stents.

The management of major airway collapse in the pediatric age group has evolved and continues to evolve over time. Tracheobronchomalacia, either primary or secondary, is still the most frequent cause of major airway collapse. This article reviews tracheobronchomalacia and discusses several treatment options; from traditional aortopexy to the more recent introduction of tracheobronchial stenting. Various types of stents are discussed and the authors' preferences are included.

Bronchi↗
PubMed2000

Modulation of the phosphatase activity of calcineurin by oxidants and antioxidants in vitro.

Previous research has indicated that oxidants, antioxidants and the intracellular redox state regulate the activities of a variety of protein tyrosine kinases, protein tyrosine phosphatases, phospholipases and transcription factors. In order to explore the redox regulation of the serine/threonine phosphatase calcineurin, we have investigated the effects of a variety of oxidants and antioxidants on calcineurin phosphatase activity in vitro. The oxidants hydrogen peroxide, superoxide and glutathione disulfide inhibited the phosphatase activity of calcineurin in a dose-dependent manner. Incubation of purified calcineurin with the antioxidants ascorbate, ascorbate 2-phosphate, alpha-lipoic acid, N-acetyl-L-cysteine and glutathione increased phosphatase activity relative to untreated controls. In contrast, several other commonly used antioxidants, including butylated hydroxytoluene, butylated hydroxyanisole, TEMPOL (4-hydroxy-2,2,6, 6-tetramethylpiperidine-N-oxyl), Trolox (6-hydroxy-2,5,7, 8-tetramethyl-chroman-2-carboxylic acid) and dihydrolipoic acid decreased the activity of purified calcineurin, possibly through prooxidative mechanisms. Although the antioxidant pyrrolidine dithiocarbamate increased the activity of purified calcineurin, it significantly inhibited the activity of calcineurin present in crude fibroblast lysates. These results support and extend the hypothesis that redox factors modulate the phosphatase activity of calcineurin and suggest that further in vivo studies are warranted.

Animals↗
PubMed1999

Fetal trisomy 10 mosaicism: ultrasound, cytogenetic and morphologic findings in early pregnancy.

We report the ultrasound, cytogenetic and morphologic findings in a case of trisomy 10 mosaicism prenatally detected by chorionic villus sampling (CVS). CVS sampling was carried out at the 13th week of gestation because of ultrasound diagnosis of hydrops fetalis and hygroma colli. Trisomy 10 mosaicism was diagnosed in cells from the cytotrophoblast (short-term culture) and the chorionic villus core (long-term culture). Fetal mosaicism was confirmed after termination of pregnancy in umbilical cord cells, placenta and fetal skin fibroblasts.

Adult↗
PubMed1998

Mitochondrial DNA synthesis studied autoradiographically in various cell types in vivo.

It is generally accepted that mitochondria are able to proliferate even in postmitotic cells due to their natural turnover and also to satisfy increased cell energy requirements. However, no detailed studies are available, particularly with respect to specific cell types. Since [3H]-thymidine is incorporated not only into nuclear (n) DNA but also into the DNA of cytoplasmic mitochondria, an autoradiographic approach was developed at the light microscopy level in order to study basic questions of mitochondrial (mt) proliferation in organs of rodents in situ via the cytoplasmic incorporation of [3H]-thymidine injected into the animals 1 h before sacrifice. Experiments carried out on mice after X-irradiation showed that cytoplasmic labeling was not due to a process such as unscheduled nuclear DNA synthesis (nUDS). Furthermore, half-lives of mitochondria between 8-23 days were deduced specifically in relation to cell types. The phase of mtDNA synthesis was about 75 min. Finally, mt proliferation was measured in brain cells of mice as a function of age. While all neurons showed a decreasing extent of mtDNA synthesis during old age, nUDS decreased only in distinct cell types of the cortex and hippocampus. We conclude that the leading theories explaining the phenomenon of aging are closely related, i.e., aging is due to a decreasing capacity of nDNA repair, which leads to unrepaired nDNA damage, or to an accumulation of mitochondria with damaged mtDNA, which leads to a deficit of cellular energy production.

Aging↗
PubMed1996

A possible tyrosine phosphorylation of phytochrome.

Red/far-red light signal transduction by the phytochrome family of photoreceptors regulates plant growth and development. We investigated the possibility that tyrosine kinases and/or phosphatases are involved in phytochrome-mediated signal transduction using crude extracts of oat seedlings that are grown in the dark. We found that a 124 kDa protein was tyrosine-phosphorylated as determined by Western blotting with a phosphotyrosine-specific monoclonal antibody. The 124 kDa protein was recognized by the anti-phosphotyrosine antibody in anti-phytochrome A immunoprecipitates. The level of anti-phosphotyrosine antibody binding to the 124 kDa protein(s) in phytochrome immunoprecipitates that had been treated with red light prior to immunoprecipitation decreased relative to dark controls. These results suggest that either phytochrome from dark-grown seedlings is tyrosine phosphorylated or that it co-immunoprecipitates with a phosphotyrosine-containing protein of the same molecular weight. The implications of these results in the regulation of (a) the putative Ser/Thr kinase activity of the photoreceptor and (b) the binding of signaling molecules, such as phospholipase C to phytochrome, are discussed.

Antibodies, Monoclonal↗
PubMed1996

Light signal transduction mediated by phytochromes: preliminary studies and possible approaches.

Phytochromes mediate a variety of developmental and growth processes involved in the photomorphogenesis of plants. In this article, we review the current understanding of the structure and function of the photoreceptor, discuss some very preliminary results, and offer speculations and even conjectures that may elicit future studies into the molecular mechanisms of the phytochrome-mediated light signal transduction in plants.

Light↗
PubMed1995

Factors affecting herd milk composition and milk plasmin at four levels of somatic cell counts.

A longitudinal study was carried out on samples of bulk tank milk collected from 200 farms for 12 mo to evaluate SCC, plasmin and plasminogen activities, psychrotrophic bacteria count, and protein quality in milk and to examine the proteolytic effects of plasmin on milk proteins. Herds were selected randomly from client lists of two dairies to create four groups based on milk SCC of the month before the study; herds were reassigned monthly to one of four groups based on SCC for that month. Overall means were 3.73% fat, 3.13% protein by infrared analysis, 3.16% protein by Kjeldahl analysis, 2.42% casein percentage, 4.65% lactose, 5.43 cells/ml of log SCC, 1.13 U of plasmin, 45.6 U of plasminogen, and log 2.86 cfu/ml of psychrotrophic bacteria. The ANOVA showed a significant effect of month on all factors except SCC, which was fixed by the experimental design. Plasmin and plasminogen activities were high from December to May. Plasmin activities and psychrotroph counts were significantly higher for the high SCC group. Casein percentage and number were significantly higher for the low SCC group.

Animals↗
PubMed1994

A plant nucleoside diphosphate kinase homologous to the human Nm23 gene product: purification and characterization.

Nucleoside diphosphate kinases (NDPKs) catalyze the transfer of high-energy phosphates from nucleoside triphosphates to nucleoside diphosphates and may be involved in the regulation of growth, development, and signal transduction processes. We report here the purification and characterization of NDPK from detergent-solubilized extracts of dark-grown oat (Avena) tissue. The purification was achieved primarily through adsorption to GTP-agarose, followed by elution with ATP. SDS-polyacrylamide gel electrophoresis and gel filtration chromatography indicated that the purified protein is composed of six 18 kDa subunits. Substrate specificity experiments indicated that the purified kinase is capable of using all tested nucleosides as substrates. N-terminal sequencing of the Avena protein revealed that 87% of the 23 amino acids sequenced were identical to the human Nm23 protein, a nucleoside diphosphate kinase identified as a possible tumor metastasis suppressor and transcriptional activator of the myc oncogene.

Amino Acid Sequence↗
PubMed1994

Isolation and purification of a small-molecular-weight GTP-binding protein from plants.

As part of testing the hypothesis that signal transduction in higher plants is mediated by G-protein(s), a 24-kDa GTP-binding protein was isolated and purified to near homogeneity from 3.5-day-old dark grown oat (Avena) seedlings by hydroxyapatite, GTP-agarose, and Sephacryl S-200 chromatographies. The protein bound maximally 0.9 +/- 0.1 mol of [35S]guanosine 5'-(3-O-thio) triphosphate (GTP gamma S)/mol of protein with an apparent Kd of approximately 32 nM. Although binding of [35S]GTP gamma S was inhibited by both GTP and GDP, no inhibition of [35S]GTP gamma S binding was observed in the presence of ATP, UTP, CTP, ITP, or TTP. The 24-kDa protein hydrolyzed GTP with a rate of 0.06 mol Pi/mol protein/min. The results suggest that this GTP-binding protein is a unique plant GTP-binding protein that exhibits characteristics similar to those of animal ras-related GTP-binding proteins.

Adenosine Diphosphate Ribose↗
PubMed1991

G-proteins in etiolated Avena seedlings. Possible phytochrome regulation.

The molecular mechanism of light signal transduction in plants mediated by the photosensor phytochrome is not well understood. The possibility that phytochrome initiates the signal transduction chain by modulating a G-protein-like receptor is examined in the present work. Etiolated Avena seedlings contain G-proteins as examined in terms of the binding of GTP as well as by cross-reaction with mammalian G-protein antibodies. The binding of GTP was regulated in vivo by red/far-red light. The possible involvement of G-proteins in the phytochrome-mediated signal transduction in etiolated Avena seedlings has been implicated from the study of the light regulated expression of the Cab and phy genes.

Adenosine Diphosphate Ribose↗
PubMed1990

Chromophore topography and secondary structure of 124-kilodalton Avena phytochrome probed by Zn2(+)-induced chromophore modification.

The relative extent of chromophore exposure of the red-absorbing (Pr) and far-red-absorbing (Pfr) forms of 124-kDa oat phytochrome and the secondary structure of the phytochrome apoprotein have been investigated by using zinc-induced modification of the phytochrome chromophore. The absence of bleaching of Pr in the presence of a 1:1 stoichiometric ratio of zinc ions, in contrast to extensive spectral bleaching of the Pfr form, confirms previous reports of differential exposure of the Pfr chromophore relative to the Pr chromophore [Hahn et al. (1984) Plant Physiol. 74, 755-758]. The emission of orange fluorescence by zinc-chelated Pfr indicates that the Pfr chromophore has been modified from its native extended/semi-extended conformation to a cyclohelical conformation. Circular dichroism (CD) analyses of native phytochrome in 20 mM Tris buffer suggests that the Pr-to-Pfr phototransformation is accompanied by a photoreversible change in the far-UV region consistent with an increase in the alpha-helical folding of the apoprotein. The secondary structure of phytochrome in Tris buffer, as determined by CD, differs slightly from that of phytochrome in phosphate buffer, suggesting that phytochrome is a conformationally flexible molecule. Upon the addition of a 1:1 molar ratio of zinc ions to phytochrome, a dramatic change in the CD of the Pfr form is observed, while the CD spectrum of the Pf form is unaffected. Analysis of the bleached Pfr CD spectrum by the method of Chang et al. (1978) reveals that chelation with zinc ions significantly alters the secondary structure of the phytochrome molecule, specifically by increasing the beta-sheet content primarily at the expense of alpha-helical folding.(ABSTRACT TRUNCATED AT 250 WORDS)

Circular Dichroism↗
PubMed1988

Non-responsiveness to hepatitis-B vaccination: revaccination and immunogenetic typing.

The variation in immune responses to standard inoculation of the hepatitis-B virus vaccine suggest that host factors influence response in ways that are not presently understood. We studied 25 low/nonresponding health care workers (anti-HBs titer less than 50 IU/l) after the third inoculation of an experimental hepatitis-B vaccine to determine their immune status (through lymphocyte phenotypes) and HLA type. After application of a fourth inoculation, the seroconverting subjects showed only low anti-HBs levels; three male subjects remained anti-HBs negative. Twelve months after the fourth inoculation only 9 of 25 subjects (36%) maintained anti-HBs titer greater than 10 IU/l. Almost all subjects had normal B-cell and CD-4 and CD-8 counts and ratios. Relative to other European populations HLA-A-10 (P less than 0.05), B-12 (P less than 0.025), CW-5 (P less than 0.05), DR-3 (P less than 0.025), and DR-5 (P less than 0.025) were increased, whereas DR-2 (P less than 0.05) was decreased. However, after correction of the P-values for the number of HLA antigens determined, these differences were no longer significant. Furthermore, these HLA types were not the same as those reported in other studies (except for DR-3). We suggest that larger sample sizes or even not yet available immunogenetic markers will be required to prove an "immunogenetic background" in low/nonresponders, if it exists.

Adolescent↗
PubMed1988

Complexity of the early genetic response to growth factors in mouse fibroblasts.

Genes whose expression is growth factor regulated are likely to be important components in the mechanisms controlling cell proliferation and differentiation. With the aim of identifying some of those genes, a lambda cDNA library was prepared with poly(A)+ RNA from quiescent NIH 3T3 cells stimulated with serum for 4 h in the presence of cycloheximide. Differential screening of approximately 200,000 recombinant phage plaques revealed 2,540 clones that cross hybridized preferentially with [32P]cDNA derived from RNA of stimulated cells rather than with cDNA derived from nonstimulated cells. Cross hybridization of these clones identified 82 independent sequences, including c-fos and c-myc. Seventy-one clones were further studied. Analysis of the changes in transcription and mRNA levels after serum stimulation demonstrated that the kinetics and extent of the induction vary dramatically between the different genes. Cycloheximide in all cases superinduced the mRNA levels by two mechanisms, inhibiting the shutoff of transcription and prolonging the half-lives of the mRNAs. Our results showed that induction of proliferation is accompanied by the onset of a complex genetic program.

Animals↗