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W Stremmel

Publications and source records attributed to W Stremmel.

At least 127 records · Page 7Linked to original sources
PubMed1997

Direct evidence for catalase as the predominant H2O2 -removing enzyme in human erythrocytes.

Decomposition of hydrogen peroxide (H2O2 ) at physiological levels was studied in human erythrocytes by means of a recently developed sensitive H2O2 assay. The exponential decay of H2O2 in the presence of purified erythrocyte catalase was followed down to 10(-9) mol/L H2O2 at pH 7.4. H2O2 decomposition by purified erythrocyte glutathione peroxidase (GPO) could be directly observed down to 10(-7) mol/L H2O2 . No enzyme inhibition was observed at these low H2O2 concentrations. Catalase and GPO activities can be determined separately in a titrated mixture of purified enzymes, which simulates the conditions of H2O2 removal by the erythrocyte. Experiments with fresh human hemolysate allowed us to determine H2O2 decomposition by catalase and GPO using these enzymes in their original quantitative ratio. The different kinetics of these enzymes are shown: H2O2 decomposition by catalase depends linearly on H2O2 concentration, whereas that by GPO becomes saturated at concentrations above 10(-6) mol/L H2O2. Even at very low H2O2 concentrations GPO reaches only approximately 8% of the rate at which catalase simultaneously degrades H2O2. These data indicate an almost exclusive role for catalase in the removal of H2O2 in normal human erythrocytes.

Catalase↗
PubMed1997

Reactive oxygen intermediates are involved in the induction of CD95 ligand mRNA expression by cytostatic drugs in hepatoma cells.

Oxidative stress has been associated with the induction of programmed cell death. The CD95 ligand/receptor system is a specific mediator of apoptosis. We have used the model of drug-induced apoptosis to assess whether the CD95 ligand mRNA is induced by reactive oxygen intermediates. Treatment of HepG2 hepatoma cells with bleomycin induced the production of reactive oxygen intermediates and, as an additional parameter of oxidative stress, resulted in glutathione (GSH) depletion. In parallel, CD95 ligand mRNA expression was induced. In a similar fashion CD95 ligand mRNA expression increased after treatment with H2O2. Additional treatment with the antioxidant and GSH precursor N-acetylcysteine resulted in partial restoration of intracellular GSH levels and in reduced induction of CD95 ligand mRNA. Induction of CD95 ligand mRNA by bleomycin was further reduced by combined treatment with N-acetylcysteine and deferoxamine. These data suggest a direct role of oxygen radicals in the induction of the CD95 ligand.

Acetylcysteine↗
PubMed1997

Differences in the regulation of iron regulatory protein-1 (IRP-1) by extra- and intracellular oxidative stress.

We have studied the responses of iron regulatory protein-1 (IRP-1) to extra- and intracellular sources of reactive oxygen intermediates (ROIs). IRP-1 is a cytoplasmic RNA-binding protein that regulates iron metabolism following its activation by iron deficiency, nitric oxide, and administration of H2O2 or antimycin A, an inhibitor of the respiratory chain (Hentze, M. W., and Kühn, L. C. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 8175-8182). We show that 10 microM H2O2 suffice for complete IRP-1 activation within 60 min when H2O2 is generated extracellularly at steady-state. By contrast, rapid cellular H2O2 degradation necessitates a 5-10-fold higher bolus dose. To study IRP-1 responses to intracellular oxidative stress, mitochondrial respiration was inhibited with antimycin A (to generate oxidative stress by leakage of ROIs from complex III), or catalase was blocked with 3-amino-1,2,4-triazole (to diminish H2O2 degradation); in parallel, 2',7'-dichlorodihydrofluorescein diacetate was used as a redox-sensitive probe to monitor intracellular H2O2 levels by fluorescence-activated cell sorting. Catalase inhibition elevates intracellular H2O2, but surprisingly does not cause concomitant IRP-1 activation. Following antimycin A treatment, IRP-1 is activated, but the activation kinetics lag behind the rapid increase in detectable intracellular H2O2. IRP-1 is thus activated both by extra- and intracellular generation of ROIs. While extracellular H2O2 rapidly activates IRP-1 even without detectable increases in intracellular H2O2, intracellular H2O2 elevation is not sufficient for IRP-1 activation. IRP-1 thus represents a novel example of an H2O2-regulated protein that responds differentially to alterations of extra- and intracellular H2O2 levels. Our data also suggest that a direct attack on the 4Fe-4S cluster of IRP-1 by H2O2 (or an H2O2-derived reactive species) represents an unlikely explanation for IRP-1 activation by oxidative stress.

Acetylcysteine↗
PubMed1997

pH-independent uptake of hepatitis B virus in primary human hepatocytes.

The replication cycle of the hepatitis B virus (HBV) is still incompletely understood. In particular, the early steps of the viral life cycle, such as absorption, penetration, uncoating, and nuclear translocation require further clarification. In this study we performed infection experiments with HBV in primary human hepatocyte cultures. To further elucidate the possible mechanism of virus uptake, infection experiments were performed at different pH levels, after pretreatment of viral particles with acidic buffers and in the presence of lysosomotropic agents (chloroquine and ammonium chloride, respectively). Using a selective PCR technique which discriminates between input virus DNA and the earliest replicative form, we could demonstrate viral replication 36 hr after inoculation. HBV was taken up most efficiently at a pH of 7.4. Infection was still successful after pretreatment of viral particles at low pH and was unaffected by the presence of lysosomotropic agents. In conclusion, this suggests HBV to be a pH-independent virus.

Cells, Cultured↗
PubMed1997

Determination of catalase activity at physiological hydrogen peroxide concentrations.

A method for the determination of catalase activity (EC 1.11.1.6.) in homogenates and cell suspensions is described by following the decomposition of H2O2 at physiological H2O2 levels. This first chemiluminescence assay for catalase activity is based on the reaction of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) and NaOCl. The chemiluminescence of this reaction specifically depends on the H2O2 concentration and shows fast kinetics of less than 2 s. Using a flow technique, the exponential decay of H2O2 in the presence of catalase is followed down to 10(-8) M H2O2 at pH 7.4 over three orders of magnitude. At these very low H2O2 concentrations neither oxygen is liberated in gaseous form nor enzyme inactivation or loss of cell viability is observed. Addition of the catalase inhibitor NaN3 completely inhibits H2O2 decomposition. Since the method is not influenced by sulfhydryl and amino group containing compounds, it is especially suited for crude tissue homogenates and suspensions of intact cells. Interestingly, application to cell suspensions shows that intact human erythrocytes and rat hepatocytes exhibit only 5.8 and 1.9% of catalase activity when compared to homogenized cells. These data suggest that the diffusion of H2O2 through membranes is lower than that assumed so far.

Animals↗
PubMed1997

Drug-induced apoptosis in hepatoma cells is mediated by the CD95 (APO-1/Fas) receptor/ligand system and involves activation of wild-type p53.

Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug-sensitive cells. We investigated the mechanism of bleomycin-induced cytotoxicity in hepatoma cells. At concentrations present in the sera of patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Huh7) or in hepatoma cells which were p53-/- (Hep3B). In addition, sensitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2 cells had the same effect. In contrast, bleomycin did not enhance susceptibility towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furthermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere with CD95 receptor/ligand interaction. These data suggest that apoptosis induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to other anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the explanation of drug sensitivity and resistance.

Antibodies, Blocking↗
PubMed1997

Muscarinic acetylcholine receptor stimulation of biliary epithelial cells and its effect on bile secretion in the isolated perfused liver [corrected].

The aim was to explore whether biliary epithelial cells show muscarinic acetylcholine receptors and to investigate their role in ductular bile formation. In both, isolated rat biliary epithelial cells and Mz-Cha-1 cells, a biliary epithelial cell line, binding of [3H]N-methyl-scopolamine occurred with 0.718 +/- 0.08 and 0.482 +/- 0.05 fmol per 10(6) cells, respectively. To characterize the involved second messenger, intracellular Ca2+ levels were monitored by confocal microscopy. Stimulation of biliary epithelial cells with carbachol produced an increase in free cytosolic Ca2+ levels that declined to baseline values describing a sinusoidal oscillation curve. Increasing concentrations of the agonist decreased latency of the response and increased oscillation frequency. Similar results were obtained in Mz-Cha-1 cells. The intracellular Ca2+ originated from IP3 sensitive intracellular stores and from the extracellular medium. The Ca2+ response could partially be blocked by atropine and completely by pirenzepine, a specific muscarinic receptor-type M1 antagonist. The presence of M1 receptor messenger RNA (mRNA) in biliary epithelial cells was confirmed by reverse transcriptase polymerase chain reaction. In the isolated perfused guinea pig liver, a model with high ductular bile flow, carbachol induced a dose dependent decrease of bile flow by 79.6% +/- 9.8% at 50 mumol/L carbachol (P < .001), without affecting perfusion pressure or biliary electrolyte concentrations. It is concluded that biliary epithelial cells express muscarinic acetylcholine receptors. Stimulation of this receptor leads to cholestasis. This could be because of changes in peribiliary permeability and/or inhibition of biliary epithelial cell secretory function.

Animals↗
PubMed1997

Elevated serum levels and reduced immunohistochemical expression of thrombomodulin in active ulcerative colitis.

BACKGROUND & AIMS: The pathogenesis of ulcerative colitis and Crohn's disease is still unclear. Vascular injury has been suggested as a potential pathogenetic mechanism. Serum thrombomodulin is a marker of endothelial cell injury. The aim of this study was to determine the relevance of increased serum thrombomodulin levels for assessing disease activity in inflammatory bowel disease. As a potential cause of serum thrombomodulin level increase, the loss of local vascular thrombomodulin expression was investigated immunohistochemically. METHODS: Thrombomodulin levels were determined by enzyme-linked immunosorbent assay in sera from patients with ulcerative colitis, Crohn's disease, Schistosoma mansoni infection, and infectious diarrhea and controls. The vascular expression of thrombomodulin was investigated immunohistochemically in fresh frozen transmural specimens of normal, Crohn's, and ulcerative colitis bowel samples. RESULTS: Significantly elevated serum thrombomodulin levels were only detected in active ulcerative colitis and infectious diarrhea complicated by septicemia. A marked and general loss of vascular endothelial cell thrombomodulin expression was found immunohistochemically in inflamed bowel tissues. Graded by a newly established thrombomodulin staining index, this was significantly more marked in ulcerative colitis than Crohn's disease. CONCLUSIONS: Serum thrombomodulin proved to be a novel marker of disease activity in ulcerative colitis closely related to local vascular endothelial cell damage, which might be a relevant pathophysiological feature of ulcerative colitis.

Adult↗
PubMed1997

Clinical presentation of GB-C virus infection in drug abusers with chronic hepatitis C.

BACKGROUND/AIMS: Recently, the hepatitis GB-C virus (GBV-C) has been identified as another virus potentially causing chronic hepatitis. Although high rates of coinfection are emerging in drug addicts with chronic hepatitis C virus infection, no detailed data on clinical presentation are available. Therefore, co-infection was sought in hepatitis C virus patients to determine the impact of GB-C virus on clinical presentation. METHODS: GBV-C was determined by nested reverse transcriptase-polymerase chain reaction in serum of 70 HIV negative intravenous drug abusers with chronic hepatitis C. Biochemical, histological and virological parameters were compared between patients with or without GBV-C coinfection. RESULTS: Hepatitis C virus and GBV-C coinfection was found in 18 of 70 (25.7%) patients. Cases with coinfection were younger and had shorter duration of disease (31.4+/-6.2 vs. 35.3+/-7.3 (p=0.09) and 9.9+/-6.8 vs. 12.9+/-7.7 (p=0.17) years) than those without coinfection. Neither hepatitis C virus genotype distribution and HCV RNA levels nor serum liver function tests, titers of immunoglobulins or autoantibodies differed between the two groups. Histologically, chronic active hepatitis (16.7 vs. 46.4%, p=0.07), fibrosis (8.3% vs. 21.4%, p=0.3), and cirrhosis (0% vs. 8.2%, p=0.31) were less prevalent in coinfected patients. After interferon treatment, 5/6 coinfected and 11/19 patients with hepatitis C virus infection alone had cleared HCV RNA and 4/6 lost GBV-C RNA from serum. The two patients with GBV-C/HCV infection who persistently cleared hepatitis C virus but not GBV-C from serum had normal transaminases during follow-up despite persistence of GBV-C. CONCLUSIONS: Coinfection of chronic hepatitis C patients with GBV-C does not lead to a significant change in clinical presentation, severity of liver disease, hepatitis C viremia, or response to interferon treatment.

Adult↗
PubMed1997

Efficacy of ursodeoxycholic acid treatment and endoscopic dilation of major duct stenoses in primary sclerosing cholangitis. An 8-year prospective study.

BACKGROUND/AIMS: Primary sclerosing cholangitis is characterized by progressive fibrotic inflammation and obliteration of intra- and extrahepatic bile ducts. Ursodeoxycholic acid treatment leads to improvement of biochemical parameters of cholestasis and in part also of liver histology. During treatment, obstruction of major ducts may lead to deterioration of liver function, which may be prevented by endoscopic dilation of the stenoses. Controlled trials for evaluation of the beneficial effects of ursodeoxycholic acid treatment and of endoscopic measures in patients with major duct stenoses have become clinically difficult. Estimation of survival probabilities without treatment allows comparison of actuarial survival with the estimated survival probabilities. METHODS/RESULTS: We studied survival in 65 patients with PSC treated with ursodeoxycholic acid (750 mg/day) and by endoscopic measures whenever necessary. Patients with decompensated cirrhosis in whom transplantation was foreseen were excluded. The study was started in May 1987 and the mean follow-up period was 45.0+/-3.5 (mean+/-SEM) months. Liver histology was performed in each of the patients before entry into the study and revealed that 21% were in stage 1, 37% in stage 2, 21% in stage 3 and 20% in stage 4. Of 65 patients, 12 had major duct stenosis at entry and another 11 developed major duct stenosis during ursodeoxycholic acid treatment, which was successfully treated by repeated endoscopic balloon dilations. The actuarial Kaplan-Meier survival probabilities without liver transplantation after treatment with ursodeoxycholic acid and dilation of major duct stenoses were significantly improved compared to the predicted survival rates with p=0.001. CONCLUSIONS: Ursodeoxycholic acid does not prevent major bile duct occlusion. When ursodeoxycholic acid treatment and endoscopic opening of duct stenoses are combined, survival may be significantly improved.

Adolescent↗
PubMed1997

Final results of a phase III clinical trial on adjuvant intraportal infusion with heparin and 5-fluorouracil (5-FU) in resectable colon cancer (EORTC GITCCG 1983-1987). European Organization for Research and Treatment of Cancer. Gastrointestinal Tract Cancer Cooperative Group.

In this phase III clinical trial conducted by the Gastrointestinal Tract Cancer Cooperative Group of the European Organization for Research and Treatment of Cancer (GITCCG-EORTC), we evaluated the effect of adjuvant intraportal infusion of heparin (HEP) and 5-fluorouracil (5-FU) on overall survival, disease-free survival and time to progression in patients with resectable colon cancer. From January 1983 to June 1987, 235 patients were randomised from 14 institutions in seven European countries: 79 patients made up the control group (control): 72 the portal vein infusion group given heparin alone (5000 IU daily x 7 consecutive days) (HEP); 84 the portal vein infusion group given heparin (5000 IU daily x 7 consecutive days) and 5-FU (500 mg/m2 daily x 7 consecutive days) (HEP/5-FU); 34 patients were considered ineligible. The 199 patients considered eligible were well balanced for age, sex, Karnofsky index, tumour location, surgery, surgical procedure and Dukes' stage. Four patients (2 control, 1 HEP, 1 HEP/5-FU) died of surgical complications. No differences were observed between control group and treatment groups (HEP, HEP/5-FU) for postoperative complications and number of hospitalisation days. Severe toxicity (grade 3-4, WHO) was found in 12% of patients in the HEP group and 8% in the HEP/5-FU group. After a median follow-up of 9 years, disease progression was reported in 40% of patients in the control group, 40% in the HEP group and 29% in the HEP/5-FU group. Five-year survival, time to progression and disease-free survival were 69%, 58% and 56%, respectively, in the control arm, 61%, 58% and 56% in the HEP arm, and 71%, 69% and 65% in the HEP/5-FU arm. Based on all randomised patients, the effect of treatment was not statistically significant with respect to any of the endpoints. It is confirmed that intraportal 5-FU infusion is safe and has a tolerable toxicity, but cannot be considered standard treatment for patients with resectable colon cancer.

Adult↗
PubMed1997

Serum antibodies against Helicobacter pylori proteins VacA and CagA are associated with increased risk for gastric adenocarcinoma.

Infection with Helicobacter pylori is associated with the development of gastric cancer. To study whether the infection with H. pylori strains expressing the vacuolating cytotoxin (VacA) and/or the cytotoxin-associated protein (CagA) is associated with an increased risk of developing gastric adenocarcinoma, sera of 90 patients with gastric cancer and 90 matched controls with cardiovascular diseases were investigated for the presence of antibodies to VacA and CagA by immunoblot. Although no significant difference in the overall H. pylori seropositivity was found between cancer patients and controls, antibodies against VacA or CagA were significantly more frequent in cancer patients than in control subjects. Seventy-five (97.4%) of 77 H. pylori-positive patients in the cancer group, but only 60 (84.5%) of 71 H pylori-positive control patients had antibodies against either VacA or CagA (chi 2 = 6.63; relative risk, 2.00; 95% confidence interval, 1.18-3.39; P = 0.01). The presence of antibodies against VacA or CagA alone was also associated with an increased cancer risk (92.2% vs 80.3%; chi 2 = 5.30; relative risk, 1.74; 95% confidence interval, 1.08-2.78; P = 0.021, for VacA; and 87.0% vs 74.6%; chi 2 = 4.90; relative risk, 1.61; 95% confidence interval, 1.06-2.45; P = 0.037, for CagA). The relative risk for gastric cancer was mainly elevated in patients under 65 years, but not in patients at or over 65 years. There is evidence that infection with VacA- or CagA-producing H. pylori strains increases the risk of developing gastric cancer, especially in younger patients.

Adenocarcinoma↗
PubMed1997

Primary hepatic high-grade non-Hodgkin's lymphoma and chronic hepatitis C infection.

Little is known about the coincidence of hepatitis C virus infection (HCV) and non-Hodgkin's lymphoma, although there is an increased incidence of chronic HCV infection with cryoglobulinemia type II and, interestingly, low-grade non-Hodgkin's lymphoma (NHL) in a few patients. We therefore report on a 74-year-old white male with known chronic hepatitis C virus infection who was admitted to the clinic due to weight loss and pain in the right upper quadrant. Ultrasound examination was performed for suspected hepatocellular carcinoma since a lesion in the left lobe of the liver was seen. X-ray of the lungs showed a few scattered lesions, suggestive of metastases. The ultrasound-guided fine-needle puncture revealed a high-grade malignant B-cell NHL While alpha-fetoprotein was normal, both cryoglobulin type II and the polymerase chain reaction (PCR) for HCV were positive. After six cycles of chemotherapy consisting of CHOP, the patient showed complete remission over three years. Ultimately, he died due to a sudden myeloic blast crisis. In summary, we discuss the possible etiopathologic role of the hepatitis viruses in the occurrence of non-Hodgkin's lymphoma. As we and others showed that HCV infects peripheral mononuclear blood cells (PBML), the infected PBML not only may be a source for reinfection after orthotopic liver transplantation, but also could be the cause for transformation and monoclonal propagation of lymphomatous tissue.

Aged↗
PubMed1997

Transjugular intrahepatic portosystemic stent shunt versus sclerotherapy plus propranolol for variceal rebleeding.

BACKGROUND & AIMS: In patients with cirrhosis of the liver, after the first variceal bleeding episode, transjugular intrahepatic portosystemic stent shunting (TIPS) and endoscopic sclerotherapy plus propranolol (ES) were compared regarding prevention of variceal rebleeding and mortality. METHODS: Eighty-three patients with cirrhosis of the liver were randomized to undergo TIPS (n = 42) or ES (n = 41). RESULTS: Median observation time was in 1.6 years in the TIPS group and 1.45 years in the ES group. Cumulative rates of rebleeding were 23% in the TIPS group and 57% in the ES group (P = 0.0001). Hepatic encephalopathy was observed in 29% of the patients in the TIPS group and in 13% of those in the ES group (P = 0.041). Cumulative rates of survival were 69% in the TIPS group and 67% in the ES group (P = 0.62). Mortality rates in both groups were positively correlated with a higher Child's classification. CONCLUSIONS: Although TIPS significantly reduced the rate of rebleeding, survival rates were not improved. Because TIPS is associated with an increased risk of encephalopathy and high rates of shunt dysfunction, which requires reintervention, the procedure cannot be recommended for elective treatment after the first variceal bleeding episode, but it is an effective therapy in patients in whom endoscopic sclerotherapy fails to control bleeding.

Adult↗
PubMed1997

[The hydro-MRT of chronic inflammatory bowel diseases].

PURPOSE: Evaluation of hydro-MRI in the diagnosis of chronic inflammatory bowel disease (IBD). MATERIAL AND METHODS: 33 patients with suspected Crohn's disease or ulcerative colitis were studied prospectively. After distension of the colon by a rectal enema, breathhold MR imaging was performed during bowel relaxation. Results were compared to the clinical diagnosis, endoscopy, barium studies and histopathology. RESULTS: 24/24 patients with active Crohn's disease were correctly diagnosed by MRI. Conversely, MRI was positive in only 2/5 patients with ulcerative colitis. In 5 patients the presence of IBD was excluded. There were no false positives. CONCLUSION: Hydro-MRI is a very reliable modality in the diagnosis of Crohn's disease. In the differentiation of Crohn's disease from ulcerative colitis, hydro-MRI seems to be a promising imaging procedure.

Adolescent↗
PubMed1997

Establishment of persistent hepatitis C virus infection and replication in vitro.

Hepatitis C virus (HCV) is a major cause of chronic viral hepatitis. Development of anti-viral strategies has been hampered by the lack of efficient cell systems to propagate HCV in vitro. To establish a long-term culture system, we tested human hepatoma (HuH7, HepG2) and porcine non-hepatoma (PK15, STE) cell lines, as well as several culture and infection conditions. As a marker for virus replication, minus-strand HCV RNA in infected cells was detected by an enhanced detection system using nested RT-PCR followed by hybridization analysis. Short-term efficiency of HCV infection (10 days) was slightly increased by addition of polyethylene glycol (PEG) and/or dimethyl sulfoxide (DMSO) to culture media during inoculation of HuH7, PK15 and STE cells, but no augmentation in long-term culture was achieved, suggesting enhanced attachment of HCV to cells rather than more efficient infection. A stabilizing effect on HCV propagation was observed for 50 days in a serum-free medium with stimulation of the low-density lipoprotein (LDL) receptor expression by lovastatin. Using partially serum-free culture conditions, long-term persistence of HCV in cells and release of virions into supernatant was achieved for up to 130 days. Infectivity of released virions in supernatants after long-term culturing (day 30-80) was shown by successful infection of fresh cells. In conclusion, supplementation with PEG, DMSO and lovastatin during inoculation did not enhance virus replication substantially, but continued stimulation of LDL-receptor expression resulted in infections which persisted for over 4 months. These data support the hypothesis of an LDL-receptor mediated uptake of HCV into cells in vitro.

Aged↗