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Biomedical subjects

S Hoffmann

Publications and source records attributed to S Hoffmann.

At least 19 recordsLinked to original sources
PubMed2002

Quantitation of hepatitis C virus RNA by third generation branched DNA-based signal amplification assay.

Quantitation of hepatitis C virus (HCV) RNA has become an important tool in different clinical settings and is used extensively for pretreatment evaluation of patients infected chronically with HCV. In this study, the performance characteristics of the third generation branched DNA-based signal amplification assay (bDNA 3.0) for HCV RNA quantitation were established. The new assay version showed an analytical specificity of 98%. Mean intra- and between-run imprecisions were 6.8 and 11.2%, respectively. The assay was linear over its entire dynamic range. Quantitation appeared to be unaffected by the genotypic variability of HCV. A comparison of bDNA 3.0 with the second generation bDNA assay calibrated against the international WHO HCV RNA standard, and the PCR-based Cobas Amplicor HCV Monitor 2.0 revealed a fairly good correlation among the assays. Twenty-nine and 11% of the paired quantitative results differed by more than log(10)0.5 (i.e. three-fold). All three assays after calibration against the WHO standard also yielded clinically comparable results with regard to the tailoring of interferon alpha/ribavirin treatment duration in patients infected by HCV genotypes 1, 4, and 5.

Adolescent↗
PubMed2002

Interference by toxic metal ions with zinc-dependent proteins involved in maintaining genomic stability.

Metal ions are essential components of biological systems; nevertheless, even essential elements may have toxic or carcinogenic properties. Thus, besides As(III) and Cd(II), also Ni(II) and Co(II) have been shown previously to disturb different types of DNA repair systems at low, non-cytotoxic concentrations. Since some metals exert high affinities for SH groups, we investigated whether zinc finger structures in DNA-binding motifs of DNA repair proteins are potential targets for toxic metal ions. The bacterial formamidopyrimidine-DNA glycosylase (Fpg protein) involved in base excision repair was inhibited by Cd(II), Cu(II) and Hg(II) with increasing efficiencies, whereas Co(II), As(III), Pb(II) and Ni(II) had no effect. Furthermore, Cd(II) still disturbed enzyme function when bound to metallothionein. Strong inhibition was also observed in the presence of phenylselenyl chloride, followed by selenocystine, while selenomethionine was not inhibitory. Regarding the mammalian XPA protein involved in the recognition of DNA lesions during nucleotide excision repair, its DNA-binding capacity was diminished by Cd(II), Cu(II), Ni(II) and Co(II), while Hg(II), Pb(II) and As(III) were ineffective. Finally, the H(2)O(2)-induced activation of the poly(ADP-ribose)polymerase (PARP) involved in DNA strand break detection and apoptosis was greatly reduced by Cd(II), Co(II), Ni(II) and As(III). Similarly, the disruption of correct p53 folding and DNA binding by Cd(II), Ni(II) and Co(II) has been shown by other authors. Therefore, zinc-dependent proteins involved in DNA repair and cell-cycle control may represent sensitive targets for some toxic metals such as Cd(II), Ni(II), Co(II) and Cu(II), as well as for some selenium compounds. Relevant mechanisms of inhibition appear to be the displacement of zinc by other transition metals as well as redox reactions leading to thiol/disulfide interchange.

Cations, Divalent↗
PubMed2002

DNA-binding of drugs used in medicinal therapies.

The interactions of various low-molecular weight substances with DNA are naturally relevant mechanisms in the cellular cycle and so also used in medicinal treatment. Depending on the particular drug structure, DNA-binding modes like groove-binding, intercalating and/or stacking, give rise to supramolecular assemblies of the polynucleotides, as well as influence the DNA-protein binding. In this review, we compare the underlying molecular structures, including general aspects of DNA sequences, with the benefit in medicinal treatment. While so far interest in this field had mainly been devoted to isolated nucleic acid/drug interactions, the present paper will focus on drug efficiencies generating and influencing supramolecular organizations and their complex sequence-dependent structure-activity codes. In particular, the attention will be directed to stereoelectronic relationships. Spatial enantioselective properties are discussed in details. As examples, the drug self-assemblies, as well as the influence of drugs on supramolecular DNA formations are described. A hypothetical connection between drug-influenced DNA-toroids and the formation of micronuclei in tissues will be interpreted.

Binding, Competitive↗
PubMed2001

Hypoxia: modulation of endothelial cell proliferation by soluble factors released by retinal cells.

A devastating complication of ischemic retinopathies is retinal neovascularization. We studied the impact on retinal endothelial cell proliferation of soluble factors released from cultured retinal glial (Müller) cells and from retinal explant cultures. Hypoxia strongly stimulated VEGF release by all types of cultures but endothelial cell growth was not further increased by the corresponding conditioned media if compared to supernatants obtained under normoxia. When the final concentration of the hypoxia-conditioned media was adjusted to the VEGF level of normoxia-conditioned media, they even inhibited endothelial cell proliferation. Inhibition may be exerted by TGF-beta 2 but TGF-beta 2 mRNA and protein expression in Müller cells were found to be down-regulated under hypoxia. We conclude that retinal endothelial cell proliferation is controlled by the balance of the amount and/or efficacy of several stimulatory and inhibitory factors.

Animals↗
PubMed2001

Structure-function studies of linear and cyclized peptide antagonists of the GnRH receptor.

Structurally new analogs of the peptidic GnRH receptor antagonist Cetrorelix as well as conformationally constrained cyclized deca- or pentapeptides were synthesized and selected peptides evaluated comprehensively. To understand how structural variations of the antagonistic peptide effect pharmacodynamic properties, binding affinities and antagonistic potencies toward the human and rat GnRH receptor were determined. Whereas large substituents in position 6 of linear peptides are compatible with high binding affinity (K(D) < 0.5 nM), all cyclized peptides except the cyclo[3-10] analog D-52391 depicted low binding affinity (K(D) > 10 nM). Binding affinity and antagonistic potency in vitro correlated for all peptides and surprisingly no discrimination between human and rat receptor proteins was observed. Since receptor residues W(101) and N(102) are involved in agonist and antagonist binding, equally potent but structurally different antagonists were tested for binding to the respective W(101)A and N(102)A mutants. In contrast to linear decapeptides, residues N(102) and W(101) are not involved in binding of D-23938 and W(101) is the critical residue for D-52391 binding. We conclude that although equally potent, peptidic GnRH receptor antagonists do have distinct interactions within the ligand binding pocket. Finally, selected antagonists were tested for testosterone suppression in male rats. The duration of testosterone suppression below castration levels differed largely from 1 day for Ganirelix to 27 days for D-23487. Systemic availability became evident as the most important parameter for in vivo efficacy.

Amino Acid Sequence↗
PubMed2001

Persistent solar influence on North Atlantic climate during the Holocene.

Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's "1500-year" cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.

Journal Article↗
PubMed2001

Nasogastric tube versus gastrostomy tube for gastric decompression in abdominal surgery: a prospective, randomized trial comparing patients' tube-related inconvenience.

BACKGROUND: Perioperative decompression of the stomach is still a common procedure and can be achieved using either nasogastric tubes (NTs) or gastrostomy tubes (GTs). While both procedures appear to be equally effective, some authors believe that NTs are less convenient for patients than GTs. However, to date, no reliable prospective data are available on this issue. METHODS: We conducted a prospective, randomized trial comparing NTs versus GTs with a total of 110 patients undergoing elective colon surgery. The primary outcome measure was the patient's tube-related inconvenience and pain, assessed in a standardized interview on day 2 after surgery and quantified by means of a visual-analog scale (VAS). A questionnaire including the EORTC QLQ-C30 and additional items regarding retrospective tube-related judgements was administered on the day of discharge and 4 weeks after discharge. Secondary endpoints were the therapy-related morbidity and general complications. RESULTS: When patients were asked which of their drainage tubes (all patients had three or four drainage tubes, such as decompression drains, urinary drains, central venous line) was most inconvenient, 43% (CI 33-53%) in the NT group reported that the NT was most inconvenient, while only 4% (CI 1-10%) of the GT patients judged the GT most inconvenient ( P<0.001, Chi(2) test). This effect was also found in VAS ratings of inconvenience and discomfort ( P<0.01). Also postoperatively (p.o.), NT patients evidenced less preference for their tube system (day 2 p.o.: 71%, CI 61-80%; 4 weeks p.o.: 66%, CI 56-75%) than did GT patients (day 2 p.o.: 94%, CI 88-98%; 4 weeks p.o.: 91% CI 84-96%); again, these differences were statistically significant ( P<0.02; Chi(2) test). No differences between groups emerged regarding global quality of life or conventional clinical outcomes. CONCLUSION: This prospective randomized trial supports the clinical observation that NT causes more subjective inconvenience than GT. In cases when a prolonged postoperative ileus is expected, decisions for a prophylactic decompressing tube system have to weigh up the possibilities of different averse clinical as well as subjective outcomes. It is then preferable to include patients' preferences in the individual decision making process (shared-decision making).

Aged↗
PubMed2001

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection.

Humanized BALB/c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen-loaded dendritic cells together with autologous PBMC from HBV-naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide-specific CTL responses against the immunodominant epitope HBc(18 - 27) were induced by HBc particle or DNA vaccination of chimera engrafted with HBV-naive PBMC. Finally, strong HBc-specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self-limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in our model and clinical studies.

Animals↗
PubMed2001

Performance characteristics of a transcription-mediated nucleic acid amplification assay for qualitative detection of hepatitis C virus RNA.

The detection of hepatitis C virus (HCV) RNA by nucleic acid amplification techniques is the method of choice to differentiate between ongoing and past infection, and can be used to monitor the course of HCV infection. In this study, we evaluated the performance characteristics of a newly developed transcription-mediated amplification (TMA)-based assay, the VERSANT HCV RNA qualitative assay, which was designed to qualitatively detect HCV RNA. Samples tested by the TMA assay included 100 HCV antibody negative sera; serial dilutions of an HCV genotype 1a panel; the WHO HCV RNA standard 76/790; an HCV genotyping panel; and 150 clinical specimens, including sera from patients who had received alpha interferon (IFN) treatment or liver transplants. TMA test results were compared with the Cobas Amplicor HCV polymerase chain reaction (PCR) assay. The analytical specificity of the HCV TMA assay was > 98%. No carry-over contaminations were observed. The assay demonstrated an analytical sensitivity of 100% at 41 HCV RNA copies/mL (genotype 1a panel) and 5 IU/mL (WHO standard), respectively. HCV genotypes and subtypes did not affect the results. Qualitative RNA detection by diagnostic Amplicor PCR and TMA was in agreement in > 97% of all 150 clinical samples tested. In our study, the TMA-based assay proved to be a specific and sensitive method for qualitative HCV RNA detection. The test may turn out to be an attractive alternative to already established techniques for HCV RNA amplification in routine clinical laboratories.

Enzyme-Linked Immunosorbent Assay↗
PubMed2001

Direct measurement of VEGF-induced nitric oxide production by choroidal endothelial cells.

Vascular endothelial growth factor (VEGF) and nitric oxide (NO) seem to be involved in the process of angiogenesis, but their interactions are not clearly understood. The aim of this study was to investigate the influence of VEGF on NO production of choroidal endothelial cells (CEC) and its importance in angiogenesis. Experiments were performed using cultured bovine CEC. Basal NO release of unstimulated CEC was measured and compared to NO release of VEGF-stimulated CEC (1, 10, and 100 ng/ml). Further, cells were pretreated with N(omega)-nitro-L-arginine methyl ester (L-NAME, 1 and 2 mM) and incubated with and without VEGF (10 ng/ml) to investigate the effect of blocking NO synthase. NO release into the medium was assessed by an amperometric NO sensor. To show the importance of NO in angiogenesis, proliferation and migration of CEC were measured after VEGF stimulation and in the presence or absence of L-NAME (1 and 2 mM). Unstimulated CEC continuously produced low levels of NO. Stimulation of the cells with VEGF resulted in a dose-dependent increase in NO release. The time course after stimulation with 10 ng/ml VEGF was characterized by a prompt initial rise up to 140% of unstimulated levels and a subsequent sustained increase over 120 min. Pretreatment with L-NAME attenuated the VEGF-induced response. L-NAME incubation alone led to a reduction in basal NO release. L-NAME also significantly diminished the VEGF-enhanced CEC proliferation and migration. The results demonstrate that VEGF enhances the formation of NO in cultured CEC. The blockade of NO production reduces CEC proliferation and migration, an effect which may be important for controlling angiogenesis, especially in reducing neovascularization in age-related macular degeneration in the eye.

Aged↗
PubMed2001

Accurate disulfide formation in Escherichia coli: overexpression and characterization of the first domain (HF6478) of the multiple Kazal-type inhibitor LEKTI.

The human hemofiltrate peptide HF6478, a putative serine proteinase inhibitor, which is part of the precursor protein LEKTI, was cloned, overexpressed, and purified. HF6478 contains two disulfide bridges with 1-4, 2-3 connectivity, sharing partial homology to Kazal-type domains and other serine proteinase inhibitors. It was expressed as thioredoxin (Trx) fusion protein, and disulfide formation occurred in the oxidative cytoplasm of Escherichia coli Origami (DE3) strain which carries a trxB(-)/gor522(-) double mutation. The soluble fusion protein was purified using metal-chelating affinity chromatography. Cleavage of the Trx fusion protein with factor Xa and subsequent purification yielded the final product in amounts sufficient for structural studies. Characterization of recombinant HF6478 was done by amino acid sequencing, mass spectrometry, capillary zone electrophoresis, and CD spectroscopy. Taking the blood filtrate peptide HF6478 as example, we present a strategy which should facilitate the expression of different extracellular proteins in the E. coli cytoplasm.

Carrier Proteins↗
PubMed2001

Binding of phage-displayed HIV-1 Tat to TAR RNA in the presence of cyclin T1.

The transactivator protein (Tat) of the human immunodeficiency virus (HIV) is a key regulatory protein in the viral replication cycle. Together with cellular cyclin T1 and an RNA element (transactivation response; TAR) located at the 5' end of all viral transcripts, it forms a ternary complex that ultimately enhances the expression of all viral genes. In this ternary complex, cyclin T1 interacts directly with Tat and TAR. The presence of cyclin T1 is essential for high TAR RNA affinity and specificity of Tat. To study protein-protein and protein-RNA interaction, we developed a phage display system that displays functional Tat on the surface of bacteriophage M13. The addition of recombinant cyclin T1 to the selections yielded a phage display system that mirrors all binding properties of the cyclin T1-Tat-TAR complex known from cell assays and biochemical studies. Phage-displayed Tat protein as well as the cyclin T1 are fully functional. The relative binding capabilities of wild-type- and mutant Tat-displaying phages show that the presence of cyclin T1 significantly reduces the importance of basic residues in the basic sequence region of Tat for its binding to TAR.

Amino Acid Sequence↗
PubMed2001

Overexpression of the human angiotensin II type 1 receptor in the rat heart augments load induced cardiac hypertrophy.

Angiotensin II is known to stimulate cardiac hypertrophy and contractility. Most angiotensin II effects are mediated via membrane bound AT1 receptors. However, the role of myocardial AT1 receptors in cardiac hypertrophy and contractility is still rarely defined. To address the hypothesis that increased myocardial AT1 receptor density causes cardiac hypertrophy apart from high blood pressure we developed a transgenic rat model which expresses the human AT1 receptor under the control of the alpha-myosin heavy-chain promoter specifically in the myocardium. Expression was identified and quantified by northern blot analysis and radioligand binding assays, demonstrating overexpression of angiotensin II receptors in the transgenic rats up to 46 times the amount seen in nontransgenic rats. Coupling of the human AT1 receptor to rat G proteins and signal transduction cascade was verified by sensitivity to GTP-gamma-S and increased sensitivity of intracellular Ca2+ [Ca2+]i to angiotensin II in fluo-3 loaded transgenic cardiomyocytes. Transgenic rats exhibited normal cardiac growth and function under baseline conditions. Pronounced hypertrophic growth and contractile responses to angiotensin II, however, were noted in transgenic rats challenged by volume and pressure overload. In summary, we generated a new transgenic rat model that exhibits an upregulated myocardial AT1 receptor density and demonstrates augmented cardiac hypertrophy and contractile response to angiotensin II after volume and pressure overload, but not under baseline conditions.

Angiotensin II↗
PubMed2001

[Physiotherapy in osteoarthritis--a review of literature on conservative therapy of knee and hip osteoarthritis].

In this review, 18 studies have been evaluated about the effectiveness of exercise therapy in the physiotherapy in osteoarthritis of hip or knee. All studies emphasised the general profit of exercise therapy compared to alternative programs (such as "health education", etc.). The effect sizes were mostly indicated to be moderate to large. There were no study comparing two or more alternative exercise programs in regard to the size of effectiveness. Only two studies gave informations about the radiographic grade of the OA. Today the effectiveness is proved only for aerobic, dynamic strengthening exercises. There were no study about the effectiveness of physiotherapy in Hip-OA.

Humans↗
PubMed2001

A procedure for evaluation and documentation of susceptibility test methods using the susceptibility of Klebsiella pneumoniae to ciprofloxacin as a model.

A new procedure for the evaluation and documentation of susceptibility test methods is described. To illustrate the procedure, four basically different susceptibility test methods were examined in a routine laboratory. The test parameter detection of decreased susceptibility to ciprofloxacin (breakpoint MIC 0.25 mg/L) among 94 selected isolates of Klebsiella pneumoniae was used. In addition to comparison of frequency histograms and regression analysis, the accuracies of the susceptibility test methods were determined using the receiver operating characteristic procedure. For each of the methods, the sensitivity (SN), specificity (SP), positive predictive value (PV+) and negative predictive value (PV-) for detection of decreased susceptibility to ciprofloxacin were calculated and plotted against a range of ciprofloxacin inhibition zones determined by the various susceptibility test methods or MICs determined by the Etest (Etest MICs). The results illustrate the accuracy and the robustness of the methods, which can be used to expose the need for training and instruction of laboratory staff. It becomes possible to optimize and justify the choice of inhibition zone breakpoints or Etest MIC breakpoints according to the SN and SP of the method employed. Furthermore, the consequences of adjustments of these breakpoints on the PV+ and PV- can be analysed and related to different clinical and epidemiological situations. We believe that our approach can be used as a model for the evaluation and documentation of susceptibility test methods in general.

Anti-Infective Agents↗
PubMed2001

Scanning force microscopy observation of tumor cells treated with hematoporphyrin IX derivatives.

Cells from human head-neck squamous cell carcinoma (hypopharynx, UMSCC11, and UMSCC22) and lung tumor (alveolus, UMSCC7) were investigated by light and scanning force microscopy (SFM) observation. In the present study a less-invasive contact mode was used to scan living cells in air covered with a thin fluid layer. The investigations were done without any pretreatment of the specimens for such observations as chemical fixation, or staining. Untreated tumor cells, and those treated with the antitumor drug hematoporphyrin IX derivative (HpD) were studied without photosensitizing. Additionally, the temperature influence on cell proliferation was studied. Three-dimensional topographic images and their magnifications offer highly informative insights into the untreated cell surface. In the present study, the cell structure destruction and cell death could partly be visualized by observing the head-neck tumor cells incubated with HpD. Most of the drug-treated head-neck tumor cells died (only 2%-5% of survivors). However, HpD could not affect cells of the lung tumor cell type. They, well known as more resistant against oxidation processes, survived to a great extent. Also, no distortion of the membrane under drug treatment could be observed. The possibilities and limits in the use of SFM for studying the topography of cell surfaces are presented in many details.

Antineoplastic Agents↗
PubMed2001

Phosphatidylcholine molecular species in lung surfactant: composition in relation to respiratory rate and lung development.

Surfactant reduces surface tension at the air-liquid interface of lung alveoli. While dipalmitoylphosphatidylcholine (PC16:0/ 16:0) is its main component, proteins and other phospholipids contribute to the dynamic properties and homeostasis of alveolar surfactant. Among these components are significant amounts of palmitoylmyristoylphosphatidylcholine (PC16:0/ 14:0) and palmitoylpalmitoleoylphosphatidylcholine (PC16:0/ 16:1), whereas in surfactant from the rigid tubular bird lung, PC16:0/14:0 is absent and PC16:0/16:1 strongly diminished. We therefore hypothesized that the concentrations of PC16:0/14:0 and PC16:0/16:1 in surfactants correlate with differences in the respiratory physiology of mammalian species. In surfactants from newborn and adult mice, rats, and pigs, molar fractions of PC16:0/14:0 and PC16:0/16:1 correlated with respiratory rate. Labeling experiments with [methyl-(3)H]choline in mice and perfused rat lungs demonstrated identical alveolar proportions of total and newly synthesized PC16:0/14:0, PC16:0/16:1, and PC16:0/16:0, which were much higher than those of other phosphatidylcholine species. In surfactant from human term and preterm neonates, fractional concentrations not only of PC16:0/16:0 but also of PC16:0/14:0 and PC16:0/ 16:1 increased with maturation. Our data emphasize that PC16:0/14:0 and PC16:0/16:1 may be important surfactant components in alveolar lungs, and that their concentrations are adapted to respiratory physiology.

1,2-Dipalmitoylphosphatidylcholine↗