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Biomedical subjects

Siegfried Kropf

Publications and source records attributed to Siegfried Kropf.

16 recordsLinked to original sources
PubMed2006

Consumption of redox energy by glutathione metabolism contributes to hypoxia/ reoxygenation-induced injury in astrocytes.

The role of glutathione during ischemia/reperfusion is still a controversial issue. Glutathione should exert beneficial effects in the situation of ischemia/reperfusion due to its antioxidative potency. However, increasing survival time after transient ischemia and hypoxia has been reported for glutathione depleted cells. This work was aimed to analyse whether glutathione metabolism essentially contributes to redox energy failure and subsequent cell damage during ischemia/reperfusion. For this purpose, primary astrocyte rich cell cultures were subjected to 1 h hypoxia followed by up to 4 h reoxygenation in combination with substrate deprivation and glutathione depletion. The ability of the cells to reduce MTT was used to quantify the redox power of the cells. Inhibition of glutathione synthesis by L-buthionine-(S,R)-sulfoximine (BSO) caused depletion of cellular glutathione within 24 h and increase in MTT reduction by about 10% under normoxic conditions. Reoxygenation following 1 h of hypoxia was associated with decrease in MTT reduction which was enhanced by substrate deprivation. Glutathione depletion reduced hypoxia-induced decrease in MTT reduction. Three hours of substrate deprivation prior hypoxia resulted in lower levels of MTT reduction during reoxygenaton. Our data suggest that in situations of oxidative stress such as ischemia/reperfusion, glutathione metabolism may causes decrease of the cellular redox energy below a threshold level required for basic cellular functions finally resulting in cell injury.

Animals↗
PubMed2006

Increased frequency of cystic fibrosis transmembrane conductance regulator gene mutations in infertile males.

OBJECTIVE: To investigate the frequency of mutations of the cystic fibrosis transmembrane regulator (CFTR) gene in males with reduced sperm quality before intracytoplasmic sperm injection (ICSI). DESIGN: The nine most frequent cystic-fibrosis-causing mutations in the German population and IVS8T alleles were analyzed. SETTING: University-based centers for reproductive medicine and clinical genetics. PATIENT(S): An unselected group of 597 males with oligo-, astheno-, terato-, crypto-, oligoasthenoteratozoospermia, or azoospermia, which underwent pre-ICSI genetic counseling over a 5-year period. INTERVENTION(S): Blood samples were collected from the patients during genetic counseling. MAIN OUTCOME MEASURE(S): Frequency of mutations of CFTR gene in infertile males. RESULT(S): A heterozygous CFTR mutation was observed in 34 of 597 patients (5.70%). None of the patients had two CFTR mutations. Given that our mutation panel recognizes about 82% of heterozygotes, it can be assumed that the frequency of CFTR heterozygotes in our cohort is about 6.94%. The frequency of CFTR mutations in our cohort did not correlate with a reduced sperm count. CONCLUSION(S): The frequency of cystic fibrosis in the German population is 1:3300. Thus, a CFTR heterozygosity of 3.42% can be estimated. This indicates that in our cohort of infertile males, the frequency of CFTR heterozygosity is twofold higher than in the general population (P<.0001).

Cohort Studies↗
PubMed2005

Analysis of a single nucleotide polymorphism in codon 388 of the FGFR4 gene in malignant gliomas.

The FGFR4 codon 388 polymorphism (Arg(388), Arg/Gly(388) or Gly(388)) was determined in glioblastoma multiforme (GBM), anaplastic astrocytomas (AA), diffuse astrocytomas (DA), and control muscles. Arg(388) was rare in AA, GBM, muscles, and was absent in DA. The Arg/Gly(388) and the Gly(388) frequency was equal among GBM and controls. FGFR4 expression was not related to codon 388 in GBM, and no survival differences between Arg/Gly(388) and Gly(388) tumors were found. U87 cells (Arg/Gly(388)) did not show higher invasion than U138 cells (Gly(388)). This suggests that the FGFR4 codon 388 status does not play a major role in malignant gliomas.

Base Sequence↗
PubMed2005

Endothelial dysfunction induced by postprandial lipemia is neutralized by addition of proteins to the fatty meal.

BACKGROUND: Postprandial lipemia is known to reduce endothelium-dependent flow-mediated vasodilation (FMD). Because postprandial lipemia can be acutely mitigated when proteins are added to the fatty meal, we investigated whether this mitigation could neutralize the lipemia-induced endothelial dysfunction. DESIGN: Sixteen healthy students (aged 19-23, eight males and eight females) received three different test meals at intervals of 1 week between successive tests. Each meal contained whipping cream alone or whipping cream together with either caseinate or soy protein. The whipping cream contained 33% fat, and 3 ml (= 1 g fat) was given per kg body weight. The proteins added were either 50 g sodium caseinate or 50 g soy protein. FMD was assessed by two-dimensional ultrasonography of the brachial artery in the fasting state and 1, 2, 3, 4, 5, 6, 7, and 8h after the fatty meal. Blood was withdrawn at the same time-points from the other arm. Triglycerides, free fatty acids, and insulin were determined using routine methods, and both L-arginine and asymmetric dimethylarginine (ADMA) were determined by LC-MS. RESULTS: Postprandial lipemia reduced FMD, the reduction reaching a maximum of 58% after 3 h. This impairment of endothelial function was not observed when either of the test proteins had been added to the fatty meal (p < 0.01 for caseinate and p < 0.001 for soy protein). The effects of the protein addition were decreases in triglycerides and free fatty acids, increased insulin concentrations at all time-points, and an increased arginine/ADMA ratio between 1 and 5h after the meal, particularly in the case of the soy protein. CONCLUSION: We suggest that the neutralization of the lipemia-induced endothelial dysfunction is caused by direct and indirect effects of the proteins insulinotropy and, secondly, by an increased supply of L-arginine.

Adult↗
PubMed2005

Different activation of mitogen-activated protein kinase and Akt signaling is associated with aggressive phenotype of human meningiomas.

PURPOSE: Activation of intracellular signaling cascades has been implicated in the growth control of benign meningiomas, but their role for meningioma progression and outcome is unknown. Here we determined the expression and function of proteins involved in mitogen-activated protein kinase (MAPK) and phosphinositol-3 kinase (PI3K)/Akt signaling in benign, atypical, and malignant meningiomas and studied their association with clinicopathologic data including meningioma recurrence. EXPERIMENTAL DESIGN: Expression of various MAPK and PI3K signaling proteins was determined in 70 primary meningiomas and, if present, in recurrent tumors by immunohistochemistry and Western blotting. The expression patterns in primary and recurrent tumors were related to clinical data. The effect of MAPK and PI3K pathway inhibition on cell proliferation and apoptosis was determined using a primary malignant meningioma cell culture. RESULTS: Atypical and malignant meningiomas showed higher levels of phospho-Akt compared with benign tumors, and their proliferation could be inhibited by PI3K blocking using wortmannin. PI3K inhibition did not induce apoptosis in malignant meningioma cells. In contrast, expression of phospho-Raf and phospho-MAPK was decreased in aggressive meningiomas compared with benign tumors, but MAPK inhibition by PD98059 resulted in tumor cell apoptosis and decreased proliferation. Reduced MAPK activation was associated with meningioma recurrence, and PI3K activation was associated with poor preclinical condition and brain invasion of malignant meningiomas. CONCLUSIONS: Both MAPK and PI3K/Akt pathways are activated at different levels in benign and malignant meningiomas. Activation of PI3K/Akt signaling contributes to the aggressive behavior of malignant meningiomas, whereas MAPK activation is involved in both proliferation and apoptosis of malignant meningiomas.

Aged↗
PubMed2005

Reduced frequency of embolic signals in severe carotid stenosis with poststenotic flow velocity reduction.

BACKGROUND: We aimed to investigate the effect of poststenotic low blood flow in patients with recently symptomatic severe carotid stenosis on arterio-arterial embolism. METHODS: Analyses based on a series of 206 consecutive patients (155 men and 51 women, mean age 65.3 years) with a nondisabling ischemic event in the anterior circulation < or =30 days (median 4.5) before presentation and diagnosis of ipsilateral carotid artery stenosis/occlusion (> or =30% local diameter reduction). All patients underwent Doppler/duplex sonography, which included measurement of poststenotic flow velocity as an indicator for poststenotic blood flow as well as a 1-hour transcranial Doppler monitoring for the detection of embolic signals. RESULTS: Thirty-seven of two hundred and six patients had very severe stenosis which was associated with reduced poststenotic flow velocity (<20 cm/s systolic) in 17 patients. Probability of embolic signals increased with increasing degree of stenosis and was maximal in patients with stenoses > or =90% local diameter reduction if poststenotic flow velocity was not reduced. Reduced poststenotic flow velocity in patients with very severe stenosis was associated with a significantly lower frequency of embolic signals compared to patients with the same degree of stenosis but no velocity reduction (adjusted odds ratio 0.15, 95% confidence interval 0.025-0.897, p = 0.038, adjustment for antiplatelet medication and time since ischemia). CONCLUSIONS: Low poststenotic flow velocity behind very severe internal carotid stenosis reduces the otherwise high frequency of embolic signals in recently symptomatic patients corroborating the hypothesis that reduced blood flow across carotid stenosis causes reduced embolism.

Adult↗
PubMed2005

Tests for differentiation in gene expression using a data-driven order or weights for hypotheses.

In the analysis of gene expression by microarrays there are usually few subjects, but high-dimensional data. By means of techniques, such as the theory of spherical tests or with suitable permutation tests, it is possible to sort the endpoints or to give weights to them according to specific criteria determined by the data while controlling the multiple type I error rate. The procedures developed so far are based on a sequential analysis of weighted p-values (corresponding to the endpoints), including the most extreme situation of weighting leading to a complete order of p-values. When the data for the endpoints have approximately equal variances, these procedures show good power properties. In this paper, we consider an alternative procedure, which is based on completely sorting the endpoints, but smoothed in the sense that some perturbations in the sequence of the p-values are allowed. The procedure is relatively easy to perform, but has high power under the same restrictions as for the weight-based procedures.

Algorithms↗
PubMed2004

Gene expression analysis reveals evidence for increased expression of cell cycle-associated genes and Gq-protein-protein kinase C signaling in cold thyroid nodules.

In contrast to the molecular etiology of autonomously functioning thyroid nodules, the molecular cause of cold thyroid nodules (CTNs), their benign, functional inactive counterparts, are so far largely unknown. Because of the partially dedifferentiated phenotype of CTNs, alterations in signaling cascades that favor proliferation, but not differentiation, are likely candidates for tumor induction and progression. The importance of RAS mutations for the development of benign nodules with follicular histology is still in question. However, differentially expressed genes in the context of their signaling cascades could define aberrant signaling in CTNs. Therefore, we investigated gene expression in 22 CTNs and their normal surrounding tissue using Affymetrix GeneChips. Most prominently, data analysis revealed an increased expression of cell cycle-associated genes and a special relevance of protein kinase C signaling, whereas no evidence of RAS-MAPK signaling in CTNs was found. Moreover, we determined 31 differentially regulated genes in CTNs, including several histone mRNAs. Taken together, these results explain recent findings showing an increased proliferation in CTNs and draw attention to protein kinase C signaling, but away from RAS-MAPK signaling, as being involved in the etiology of CTNs.

Cell Cycle↗
PubMed2004

Flavanol-rich cocoa drink lowers plasma F(2)-isoprostane concentrations in humans.

Flavan-3-ols are potent antioxidants in vitro, but convincing evidence for antioxidant action in vivo is lacking. We examined whether an oxidative stress-mediated increase in plasma F(2)-isoprostanes is counteracted by a flavanol-rich cocoa beverage. Twenty volunteers were examined in a comparative randomized double-blind crossover design with respect to ingestion of high-flavanol cocoa drink (HFCD; 187 mg flavan-3-ols/100 ml) vs. low-flavanol cocoa drink (LFCD; 14 mg/100 ml). With 10 individuals, the treatment was combined with strenuous physical exercise. Total (esterified plus nonesterified) F(2)-isoprostanes were analyzed by GC/MS. LFCD caused a slight increase in the mean (+/- SEM) plasma concentrations of F(2)-isoprostanes 2 and 4 h after intake (2.16 +/- 0.19 nM at 4 h vs. 1.76 +/- 0.11 nM at 0 h, n = 10), which may be attributable to postprandial oxidative stress. This increase did not occur with HFCD (1.57 +/- 0.06 nM at 4 h vs. 1.65 +/- 0.10 nM at 0 h, n = 10). The difference in F(2)-isoprostanes 2 and 4 h after intake of HFCD vs. LFCD became statistically significant when the intake was combined with physical exercise (P < 0.01, ANOVA). We conclude that dietary flavanols, using cocoa drink as example, can lower the plasma level of F(2)-isoprostanes, indicators of in vivo lipid peroxidation.

Adult↗
PubMed2004

Time period required for transcranial Doppler monitoring of embolic signals to predict recurrent risk of embolic transient ischemic attack and stroke from arterial stenosis.

BACKGROUND AND PURPOSE: We aimed to investigate whether the time period of transcranial Doppler monitoring for embolic signals can be reduced without loss of clinical yield compared with routinely performed 1-hour monitoring. METHODS: Investigations on the basis of a post hoc analysis of a previously published cohort of 86 patients (55 men, 31 women; mean age 60.6 years) with a nondisabling arterioembolic ischemic event in the anterior circulation within the last 30 days (mean 7.3) and an ipsilateral medium-grade or high-grade stenosis of the carotid or middle cerebral artery. Patients underwent 1-hour monitoring for embolic signals and were followed up prospectively for 6 weeks to evaluate the relationship between embolic signals and risk of an early ischemic recurrence. Risk was also calculated after fictitious reduction of the monitoring period from 60 minutes to 50, 40, 30, 20, and 10 minutes, respectively, and compared with the results obtained from the 1-hour period. RESULTS: The number of patients positive for embolic signals decreased with the decreasing monitoring period. By this, the odds ratio of embolic signals for an early ischemic recurrence "decreased" from 40 (derived from the 1-hour monitoring) to 10 when the monitoring lasted < or =30 minutes. The relationship between the rate of embolic signals per hour and risk of a recurrent stroke is described by an S-shaped curve. As a consequence, risk estimated from reduced monitoring periods can differ considerably from that derived from the 1-hour monitoring if the signal frequency lies within a medium range (eg, between 3 and 15 signals in 30 minutes). CONCLUSIONS: The time period of monitoring for embolic signals may be reduced without loss of clinical relevant information when signal frequency is low or already high during the reduced monitoring period, but it should be prolonged to maximally an hour at signal numbers within a medium range. However, our results need to be externally validated on an independent cohort of patients or confirmed by a prospective study before this modification can be recommended in general.

Aged↗
PubMed2004

Gene expression analysis reveals evidence for inactivation of the TGF-beta signaling cascade in autonomously functioning thyroid nodules.

Molecular events that lead to the development of autonomously functioning thyroid nodules (AFTNs) are somatic mutations of the thyrotropin receptor (TSHR) in approximately 60% of the nodules and less frequently, somatic mutations in the Gsalpha protein. However, AFTNs without known mutations indicate that other causes remain to be identified. Moreover, the impact of constitutively activating TSHR mutations on the signal transduction network of the thyroid epithelial cell is unknown. We therefore investigated gene expression in 15 AFTNs and their surrounding tissue using Affymetrix GeneChips. Most prominently, data analysis revealed a changed pattern of gene expression in the TGF-beta signaling cascade and 25 differentially regulated genes in AFTNs, including thyroid peroxidase, type I iodothyronine deiodinase and sialyltransferase (SIAT) 1. Strikingly coexpression of SIAT 1 and TSHR in COS-7 cells increased TSH binding and cell surface expression of the TSHR. Moreover, differences in gene expression patterns for AFTNs with and without TSHR mutations indicate specific alterations of signal transduction in AFTNs without TSHR mutations. These results suggest that AFTNs with TSHR mutations harbor further mechanisms of forward stimulation. Furthermore, they give important leads to elucidate the molecular etiology of AFTNs without TSHR mutations.

Animals↗
PubMed2004

Significance test for comparing complex microbial community fingerprints using pairwise similarity measures.

Modern electrophoresis techniques are often applied to investigate complex microbial communities. Analysis systems like GelCompare transform the optical pattern of the electrophoresis lanes into high-dimensional observation vectors and calculate measures of difference or similarity between pairs of lanes. Usually, these measures are applied in cluster analyses. Here, we apply permutation tests for the comparison of groups of lanes based on these pairwise measures together with some extensions for a combined analysis of several electrophoresis gels. The procedures are available as a computer program. An example is given for the comparison of bacterial soil communities, testing the effect of different crop plants. Each community was represented by amplified ribosomal gene fragments separated in a denaturing gradient gel.

Bacteria↗
PubMed2003

Prognostic relevance of MAPK expression in glioblastoma multiforme.

The objective of this study was to determine the immunoexpression pattern of the mitogen-activated protein kinase (MAPK), and related signalling proteins [protein kinase C (PKC), phospholipase Cgamma (PLCgamma)], in glioblastoma multi-forme, and to investigate their prognostic value. Paraffin-embedded biopsy samples from 26 patients [13 patients with long-term survival (LTS; N=13; median 28 months, range 13-76 months), and, for comparison, 13 patients with short-term survival (STS; N=13; median 7 months, range 1-12 months)] were investigated for the immunoexpression of MAPK, the activated pMAPK, PKC, PLCgamma, EGFR, and PTEN. Additionally, the MIB-1 proliferation index was determined. The immunoexpression pattern were related to clinical data, including analysis of their prognostic value using the Cox-proportional hazard model. No significant differences were found between STS and LTS in terms of age, Karnofsky performance status, and treatment. Whereas EGFR expression did not differ between STS and LTS and does not influence survival, expression of MAPK and activated pMAPK was significantly correlated with survival time. The percentage of pMAPK expressing cells correlated strongly with the percentage of MIB-1 positive cells. Furthermore, survival in patients with tumors expressing PKC or PLCgamma was significantly shorter. No differences were found for PTEN expression. Our findings indicate that the MAPK pathway is correlated with proliferation in gliomas, and that patient subgroups exist, in which expression of MAPK-related signalling proteins (PKC, PLCgamma) is associated with poorer prognosis. These patient subgroups may benefit from additional chemotherapeutic agents which specifically inhibit these signalling proteins.

Adult↗
PubMed2003

Clinical studies' assessment.

The paper gives some more general remarks on clinical studies from the perspective of a biometrician. Prospective randomised clinical trials are the study type with highest evidence. But there are other study types, too, which have their legitimacy in the process of medical knowledge finding and quality assurance. It is important to use each type in the right place and in the right way. Analysis and interpretation have to take care for the study type.

Clinical Trials as Topic↗
PubMed2002

Increased pregnancy rates after ultralong postoperative therapy with gonadotropin-releasing hormone analogs in patients with endometriosis.

OBJECTIVE: To examine whether ultralong GnRH analog (GnRH-a) therapy after surgical treatment of endometriosis and before ART influences the pregnancy rate. DESIGN: Prospective, randomized, controlled study. SETTING: University clinic for reproductive medicine and gynecologic endocrinology. PATIENT(S): One hundred ten patients with stage II to IV endometriosis according to ASRM criteria. INTERVENTION(S): Fifty-five patients received GnRH-a for 6 months after surgery and subsequently underwent up to 3 cycles of ART, and 55 patients received 3 cycles of ART alone immediately after surgery. MAIN OUTCOME MEASURE(S): Clinical pregnancy rates. RESULTS: The pregnancy rate per patient was higher among patients who received follow-up treatment with GnRH-a. The same results were found in patients with stage III or IV endometriosis who were undergoing IUI or IVF/ICSI. CONCLUSION(S): Ultralong GnRH-a therapy increases the pregnancy rate of ART in patients with severe endometriosis.

Adult↗