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Biomedical subjects

Ulrich Schäfer

Publications and source records attributed to Ulrich Schäfer.

At least 19 recordsLinked to original sources
PubMed2006

Misexpression screen in Drosophila melanogaster aiming to reveal novel factors involved in formation of body parts.

To identify novel factors that lead a fly imaginal disc to adopt its developmental fate, we carried out a modular dominant misexpression screen in imaginal discs. We have identified two factors that appear to change the fate of the respective body structure and appear to lead to the transformation of a body part. In one mutant line, notum tissue, normally derived from wing imaginal tissue, formed close to the site of the sternopleural bristles, which are leg disc derivatives. In the other line, the arista is transformed into a tubular structure, resembling an abnormal leg. We found that ectopic expression of abrupt was responsible for this potential transformation of the arista.

Animals↗
PubMed2006

Cardiac mast cell-derived renin promotes local angiotensin formation, norepinephrine release, and arrhythmias in ischemia/reperfusion.

Having identified renin in cardiac mast cells, we assessed whether its release leads to cardiac dysfunction. In Langendorff-perfused guinea pig hearts, mast cell degranulation with compound 48/80 released Ang I-forming activity. This activity was blocked by the selective renin inhibitor BILA2157, indicating that renin was responsible for Ang I formation. Local generation of cardiac Ang II from mast cell-derived renin also elicited norepinephrine release from isolated sympathetic nerve terminals. This action was mediated by Ang II-type 1 (AT1) receptors. In 2 models of ischemia/reperfusion using Langendorff-perfused guinea pig and mouse hearts, a significant coronary spillover of renin and norepinephrine was observed. In both models, this was accompanied by ventricular fibrillation. Mast cell stabilization with cromolyn or lodoxamide markedly reduced active renin overflow and attenuated both norepinephrine release and arrhythmias. Similar cardioprotection was observed in guinea pig hearts treated with BILA2157 or the AT1 receptor antagonist EXP3174. Renin overflow and arrhythmias in ischemia/reperfusion were much less prominent in hearts of mast cell-deficient mice than in control hearts. Thus, mast cell-derived renin is pivotal for activating a cardiac renin-angiotensin system leading to excessive norepinephrine release in ischemia/reperfusion. Mast cell-derived renin may be a useful therapeutic target for hyperadrenergic dysfunctions, such as arrhythmias, sudden cardiac death, myocardial ischemia, and congestive heart failure.

Angiotensins↗
PubMed2006

Reconstructed human epidermis for skin absorption testing: results of the German prevalidation study.

Exposure to chemicals absorbed by the skin can threaten human health. In order to standardise the predictive testing of percutaneous absorption for regulatory purposes, the OECD adopted guideline 428, which describes methods for assessing absorption by using human and animal skin. In this study, a protocol based on the OECD principles was developed and prevalidated by using reconstructed human epidermis (RHE). The permeation of the OECD standard compounds, caffeine and testosterone, through commercially available RHE models was compared to that of human epidermis and animal skin. In comparison to human epidermis, the permeation of the chemicals was overestimated when using RHE. The following ranking of the permeation coefficients for testosterone was obtained: SkinEthic > EpiDerm, EPISKIN > human epidermis, bovine udder skin, pig skin. The ranking for caffeine was: SkinEthic, EPISKIN > bovine udder skin, EpiDerm, pig skin, human epidermis. The inter-laboratory and intra-laboratory reproducibility was good. Long and variable lag times, which are a matter of concern when using human and pig skin, did not occur with RHE. Due to the successful transfer of the protocol, it is now in the validation process.

Adult↗
PubMed2005

Identification of Drosophila genes modulating Janus kinase/signal transducer and activator of transcription signal transduction.

The JAK/STAT pathway was first identified in mammals as a signaling mechanism central to hematopoiesis and has since been shown to exert a wide range of pleiotropic effects on multiple developmental processes. Its inappropriate activation is also implicated in the development of numerous human malignancies, especially those derived from hematopoietic lineages. The JAK/STAT signaling cascade has been conserved through evolution and although the pathway identified in Drosophila has been closely examined, the full complement of genes required to correctly transduce signaling in vivo remains to be identified. We have used a dosage-sensitive dominant eye overgrowth phenotype caused by ectopic activation of the JAK/STAT pathway to screen 2267 independent, newly generated mutagenic P-element insertions. After multiple rounds of retesting, 23 interacting loci that represent genes not previously known to interact with JAK/STAT signaling have been identified. Analysis of these genes has identified three signal transduction pathways, seven potential components of the pathway itself, and six putative downstream pathway target genes. The use of forward genetics to identify loci and reverse genetic approaches to characterize them has allowed us to assemble a collection of genes whose products represent novel components and regulators of this important signal transduction cascade.

Animals↗
PubMed2005

Gain-of-function screen for genes that affect Drosophila muscle pattern formation.

This article reports the production of an EP-element insertion library with more than 3,700 unique target sites within the Drosophila melanogaster genome and its use to systematically identify genes that affect embryonic muscle pattern formation. We designed a UAS/GAL4 system to drive GAL4-responsive expression of the EP-targeted genes in developing apodeme cells to which migrating myotubes finally attach and in an intrasegmental pattern of cells that serve myotubes as a migration substrate on their way towards the apodemes. The results suggest that misexpression of more than 1.5% of the Drosophila genes can interfere with proper myotube guidance and/or muscle attachment. In addition to factors already known to participate in these processes, we identified a number of enzymes that participate in the synthesis or modification of protein carbohydrate side chains and in Ubiquitin modifications and/or the Ubiquitin-dependent degradation of proteins, suggesting that these processes are relevant for muscle pattern formation.

Animals↗
PubMed2005

Ectonucleoside triphosphate diphosphohydrolase 1/CD39, localized in neurons of human and porcine heart, modulates ATP-induced norepinephrine exocytosis.

Using a guinea pig heart synaptosomal preparation, we previously observed that norepinephrine (NE) exocytosis was attenuated by a blockade of P2X purinoceptors, potentiated by inhibition of ectonucleoside triphosphate diphosphohydrolase-1 (E-NTPDase1)/CD39, and reduced by soluble CD39, a recombinant form of human E-NTPDase1/CD39. This suggests that norepinephrine and ATP are coreleased upon depolarization of cardiac sympathetic nerve endings and that ATP enhances norepinephrine exocytosis by an action modulated by E-NTPDase1/CD39 activity. Whether E-NTPDase1/CD39 is localized to cardiac neurons and modulates norepinephrine exocytosis in intact heart tissue remained untested. We report that E-NTPDase1/CD39 is selectively localized in human and porcine cardiac neurons and that depolarization of porcine heart tissue elicits omega-conotoxin-inhibitable release of both norepinephrine and ATP. Inhibition of E-NTPDase1/CD39 with ARL67156 markedly potentiated ATP release, demonstrating that E-NTPDase1/CD39 is a major determinant of ATP availability at sympathetic nerve terminals. Notably, inhibition of E-NTPDase1/CD39 enhanced both ATP and NE exocytosis, whereas administration of soluble CD39 reduced both ATP and NE exocytosis. The strong correlation between ATP and norepinephrine release was abolished in the presence of the purinergic P2X receptor (P2XR) antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS). We conclude that released ATP governs norepinephrine exocytosis by activating presynaptic P2XR and that this action is controlled by neuronal E-NTPDase1/CD39. Clinically, excessive norepinephrine release is a major cause of arrhythmic and coronary vascular dysfunction during myocardial ischemia. By curtailing NE release, in addition to its effects as an antithrombotic agent, soluble CD39 may constitute a novel therapeutic approach to ischemic complications in the myocardium.

Adenosine Triphosphatases↗
PubMed2005

Depletion of alveolar macrophages by clodronate-liposomes aggravates ischemia-reperfusion injury of the lung.

BACKGROUND: Macrophages play an important role in ischemia-reperfusion injury of various organs. Liposome-encapsulated dichloromethylene diphosphonate (clodronate-liposome) depletes local macrophages in vivo. However, the effect of this approach on alveolar macrophages in pulmonary ischemia-reperfusion injury has not yet been evaluated. METHODS: Clodronate-liposomes in Hanks' balanced salt solution (HBSS) or HBSS alone were given intratracheally to anesthetized male Lewis rats in the clodronate or the control group (n = 6/each group). After 3 days, we subjected the lungs to ischemia (37 degrees C, 60 minutes) and reperfusion (60 minutes) in an isolated blood-perfused rat lung model. Analysis during reperfusion included gas exchange, hemodynamics, and airway mechanics. At the end of reperfusion, we determined leukocyte recruitment and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage fluid. RESULTS: In the clodronate group, 4 experiments had to be terminated within 10 minutes of reperfusion because of severe lung injury, whereas all lungs of the controls could be studied during the 60-minute reperfusion period (p < 0.05). Clodronate significantly decreased dynamic airway compliance (p < 0.05) and increased airway resistance. Besides a tendency toward greater pulmonary vascular resistance, this was associated with recruitment of polymorphonuclear neutrophils (p < 0.05) and increased MIP-2 concentrations in the bronchoalveolar lavage fluid (p < 0.05). CONCLUSIONS: Intratracheal administration of liposome-encapsulated clodronate does not benefit, but aggravates, warm ischemia-reperfusion injury of the lung, increasing MIP-2-associated alveolar neutrophil recruitment and airway mechanical dysfunction.

Animals↗
PubMed2004

Systematic gene targeting on the X chromosome of Drosophila melanogaster.

The genome of the model organism Drosophila melanogaster has been sequenced and annotated. Based on this groundwork, we performed a systematic genetic screen of the D. melanogaster X chromosome, which carries about one sixth of the genes of the organism. We generated a collection of single P-element insertions to provide genetic and molecular access to virtually all X-chromosomal genes. The study complements earlier work designed to systematically identify vital genes on the X chromosome by targeting transcription units which are phenotypically silent. We describe single UAS sequence-bearing P-element insertions throughout the X chromosome, which allows one to express the tagged genes under control of tissue/organ-directed GAL4 activity. In addition, the present collection of single insertion lines provides a tool to generate chromosomal deletions which are on average less than 33 kb in size.

Animals↗
PubMed2004

Follicle separation during Drosophila oogenesis requires the activity of the kinesin II-associated polypeptide Kap in germline cells.

Cellular localization of organelles, protein complexes and single mRNAs depends on the directed transport along microtubule tracks, a process mediated by ATP-driven molecular motor proteins of the dynein and kinesin superfamilies. Kinesin II is a heterotrimeric protein complex composed of two motor subunits and a unique nonmotor Kinesin-associated protein (Kap). Kap was shown to transport both particulate cargo, as axoneme components in rafts, and membrane-bounded organelles such as melanosomes. Drosophila Kinesin II was shown to be essential for the axonal transport of choline acetyltransferase in a specific set of neurons. We have generated Kap mutants and show that gene activity is not only required for neuronal function but also for separation of follicles during early oogenesis. The data suggest that Kap participates in the transport of signalling components required for instructive interactions between germline and soma cells.

Animals↗
PubMed2003

Erythropoietin to treat head and neck cancer patients with anaemia undergoing radiotherapy: randomised, double-blind, placebo-controlled trial.

BACKGROUND: Anaemia is associated with poor cancer control, particularly in patients undergoing radiotherapy. We investigated whether anaemia correction with epoetin beta could improve outcome of curative radiotherapy among patients with head and neck cancer. METHODS: We did a multicentre, double-blind, randomised, placebo-controlled trial in 351 patients (haemoglobin <120 g/L in women or <130 g/L in men) with carcinoma of the oral cavity, oropharynx, hypopharynx, or larynx. Patients received curative radiotherapy at 60 Gy for completely (R0) and histologically incomplete (R1) resected disease, or 70 Gy for macroscopically incompletely resected (R2) advanced disease (T3, T4, or nodal involvement) or for primary definitive treatment. All patients were assigned to subcutaneous placebo (n=171) or epoetin beta 300 IU/kg (n=180) three times weekly, from 10-14 days before and continuing throughout radiotherapy. The primary endpoint was locoregional progression-free survival. We assessed also time to locoregional progression and survival. Analysis was by intention to treat. FINDINGS: 148 (82%) patients given epoetin beta achieved haemoglobin concentrations higher than 140 g/L (women) or 150 g/L (men) compared with 26 (15%) given placebo. However, locoregional progression-free survival was poorer with epoetin beta than with placebo (adjusted relative risk 1.62 [95% CI 1.22-2.14]; p=0.0008). For locoregional progression the relative risk was 1.69 (1.16-2.47, p=0.007) and for survival was 1.39 (1.05-1.84, p=0.02). INTERPRETATION: Epoetin beta corrects anaemia but does not improve cancer control or survival. Disease control might even be impaired. Patients receiving curative cancer treatment and given erythropoietin should be studied in carefully controlled trials.

Anemia↗
PubMed2003

Predictive value of carbohydrate antigen 19-9 in pancreatic cancer treated with radiochemotherapy.

PURPOSE: To determine the predictive value of carbohydrate antigen (CA) 19-9 in pancreatic cancer treated with radiochemotherapy. METHODS AND MATERIALS: Ninety-five patients with locally advanced unresectable adenocarcinoma of the pancreas were treated with hyperfractionated accelerated radiotherapy to a total dose of 44.8 Gy combined with 5-fluorouracil and folinic acid. CA 19-9 was measured before therapy, each week during therapy, and every 4 weeks during the follow-up period. RESULTS: The median CA 19-9 before treatment was 420 U/mL; in the responder group it was 117 U/mL, and in the nonresponder group it was 806 U/mL. Patients with a pretreatment CA 19-9 less than the median had not only a significantly better tumor response (45.8%) but also a better survival prognosis (median survival 12.3 months) than those with a level higher than the median (tumor response 12.8%; median survival 7.1 months). The posttreatment median CA 19-9 for all patients also exhibited prognostic significance. The median survival of patients with a CA 19-9 level lower than the posttreatment median of 293 U/mL was 13.5 months, compared with 7.2 months for those with a CA 19-9 level greater than the median. To detect recurrent disease during follow-up, the sensitivity of CA 19-9 was 100% and the specificity 88%. CONCLUSION: Our results indicate that CA 19-9 is of predictive value for prognosis, response, and detecting recurrence of pancreatic cancer in patients undergoing combined radiochemotherapy. Therefore, we recommend the routine implementation of CA 19-9 observation during the clinical course of treatment for patients with pancreatic cancer undergoing radiochemotherapy.

Adenocarcinoma↗
PubMed2003

Selenium in the treatment of radiation-associated secondary lymphedema.

PURPOSE: The aim of this explorative study was to evaluate the impact of selenium in the treatment of lymphedema after radiotherapy. MATERIALS AND METHODS: Between June 1996 and June 2001, 12 patients with edema of the arm and 36 patients with edema of the head-and-neck region were treated with selenium for therapy-related lymphedema. Of these 36 patients, 20 had interstitial endolaryngeal edema associated with stridor and dyspnea. All patients received sodium selenite over 4 to 6 weeks. RESULTS: Self-assessment using a visual analog scale (n = 48) showed a reduction of 4.3 points when comparing pre- and posttreatment values (p < 0.05). Of 20 patients with endolaryngeal edema, 13 underwent no tracheostomy, 5 underwent a temporary tracheostomy, and only 2 underwent a permanent tracheostomy. Ten of 12 patients with arm edema showed a circumference reduction of the edematous limb and improvement in the Skin-Fold Index by 23.3 points. An improvement of one stage or more was shown by the Földi or the Miller score (n = 28) in 22 (Földi score) and in 24 (Miller score) patients. CONCLUSIONS: Treatment with sodium selenite is well tolerated and easy to deliver. Additionally, our results suggest that sodium selenite has a positive effect on secondary-developing lymphedema caused by radiation therapy alone or by irradiation after surgery.

Adult↗
PubMed2003

[Long-term results of postoperative radiotherapy for stage I endometrial carcinoma].

BACKGROUND: Surgical resection is the primary treatment in stage I endometrial carcinoma. Retrospective analyses support the value of local vaginal irradiation to avoid vaginal recurrences to be relatively proven. The impact of an additional external beam irradiation of the pelvis considering different prognostic criteria is still unclear. PATIENTS AND METHODS: From January 1986 to December 1995 a total of 128 patients with a stage I endometrial carcinoma were treated in our clinic with postoperative radiotherapy. Depending on the prognostic factors from literature, 68 patients received an HDR-brachytherapy and 60 patients a combined treatment with external beam irradiation and HDR-brachytherapy. The median follow-up was 62.1 months. The statistical analysis was performed as a retrospective cohort study. RESULTS: Depth of tumor invasion and grading could be identified as statistically significant prognostic factors for local recurrence-free and tumor-specific survival. It could be shown that an additional external beam irradiation is indicated with a tumor invasion of more than 50% of the myometrium. In the majority of cases grade I and II radiation-associated side effects were observed. Chronic side effects grade 3 and 4 at the bowel and the rectum occurred in less than 4% of cases in the combined treatment group. CONCLUSIONS: The addition of external beam irradiation to intravaginal brachytherapy is useful in tumors with more than 50% infiltration of the myometrium. Severe side effects were seen in less than 4% in combination treatment.

Adenocarcinoma↗
PubMed2003

Hemoglobin as an independent prognostic factor in the radiotherapy of head and neck tumors.

PURPOSE: The purpose of this study was to analyze the prognostic value of baseline hemoglobin levels before radiotherapy in patients with head and neck tumors. PATIENTS AND METHODS: In a retrospective study with a median follow-up of 43 months, we analyzed the results of 214 patients irradiated for head and neck cancer between January 1, 1990 and January 1, 1998 (180 men and 34 women; median age 58 years). The treatment concept consisted in adjuvant radiotherapy in 58 patients, 77 patients received definitive radiochemotherapy, 42 patients definitive radiotherapy, and 37 patients reirradiation for in-field recurrence. Baseline hemoglobin values were divided in four groups of the same patient number (quartiles). Several known prognostic factors like sex, age, tumor stage, histologic grading, performance status, and treatment scheme were analyzed for their influence on overall and event-free survival and correlated with pretreatment hemoglobin values (Kaplan-Meier method). In addition, univariate und multivariate logistic regression analyses were carried out to evaluate the effect of baseline hemoglobin on response rates. RESULTS: The median survival (event-free survival) of all patients amounted to 15 months (10 months). 25%, 50%, and 75% of patients had hemoglobin values < 11.2 g/dl, < 12.7 g/dl, and < 13.9 g/dl, respectively. In the univariate analysis, the following variables were significant prognostic factors for overall/event-free survival (log-rank test): treatment concept (p < 0.001/p < 0.001), tumor stage (p < 0.001/p < 0.001), general condition (p < 0.001/p < 0.001), and pretreatment hemoglobin (p = 0.014/p = 0.05). Multivariate analysis (Cox) proved these parameters to be independent of each other. In addition, response rate after radiation showed a strong association between hemoglobin and local control probability (p = 0.02). CONCLUSION: In this retrospective analysis, baseline hemoglobin level was shown to be an independent significant prognostic factor in radiotherapy of head and neck cancer patients. Therefore, the value of tumor anemia as a prognostic factor should be emphasized more.

Adult↗
PubMed2003

Modification of noradrenaline release in pithed spontaneously hypertensive rats by I1-binding sites in addition to alpha2-adrenoceptors.

It is known that moxonidine acts as an agonist at presynaptic alpha(2)-adrenoceptors of the postganglionic sympathetic nerve terminals and leads to a reduction in noradrenaline release. In addition, it is conceivable that I(1)-binding sites located in other regions of the pre- and postganglionic sympathetic neurons are involved in this effect. Our aim was to investigate whether and to what extent activation of the I(1)-binding sites contributes to the moxonidine-induced inhibition of noradrenaline release. Noradrenaline release was induced in pithed spontaneously hypertensive rats (pretreated with phenoxybenzamine/desipramine at 10/0.5 mg/kg) by stimulation of sympathetic overflow from the spinal cord. Noradrenaline overflow was reduced using moxonidine (0.18, 0.6, and 1.8 mg/kg) by 39.4, 70.4, or 78.7%, respectively, even when all alpha(1)-/alpha(2)-adrenoceptors were blocked effectively by phenoxybenzamine. In contrast, the I(1)-antagonist efaroxan (0.1, 1, and 3 mg/kg) increased noradrenaline overflow from 453 (control) to 1710, 1999, or 2754 pg/ml, suggesting an autoreceptor-like function of I(1)-binding sites. In consequence, moxonidine (0.18, 0.6, and 1.8 mg/kg) reduced the increase in noradrenaline overflow in efaroxan-treated animals (1 mg/kg) by 22.7, 41.7, and 50.5%, respectively. Agmatine (6 and 60 mg/kg), an endogenous agonist at I(1)-binding sites, reduced noradrenaline overflow (-36 or 53%), even under alpha(2)-adrenoceptor blockade. When 2-endo-amino-3-exo-isopropylbicyclo[2.2.1]heptane (AGN192403) (10 mg/kg) was injected, a selective blocker of I(1)-binding sites, noradrenaline overflow was not influenced by agmatine. It is concluded that moxonidine reduces noradrenaline overflow by acting at I(1)-binding sites in addition to its agonistic property at alpha(2)-adrenoceptors. The exact location of the I(1)-binding sites on the pre- or postsynaptic sympathetic neurons is unknown, but the location in the pre- or postsynaptic membrane of the sympathetic ganglion is the most plausible explanation.

Adrenergic alpha-Antagonists↗