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T Klein

Publications and source records attributed to T Klein.

At least 127 records · Page 7Linked to original sources
PubMed1996

Mechanistic studies on the selective inhibition of cyclooxygenase-2 by indanone derivatives.

The cyclooxygenase step in the conversion of arachidonic acid is a key point in the biosynthesis of prostanoids, managed by two enzymatic isoforms. In the following study we focused on the mechanism of the inhibitory action of CGP 28238 and structurally-related indanone derivatives using purified enzymes. Consistent with our earlier studies on cell systems, CGP 28238 revealed selective inhibition of cyclooxygenase-2. The process affects the bisoxygenase subunit time-dependently, and is reversible in the early phase of inhibition. From structure-activity relationships, we propose the formation of a Schiff base between the oxo-groups of CGP 28238 and an amino group at the active site providing additional binding forces for an effective inhibition of cyclooxygenase-2.

Animals↗
PubMed1996

Effect of cyclic AMP and prostaglandin E2 on the induction of nitric oxide- and prostanoid-forming pathways in cultured rat mesangial cells.

Cyclic AMP (cAMP) represents an important cellular signalling molecule. We analysed the effect of dibutyryl cAMP (db-cAMP), a cell-permeable and stable derivative of cAMP, on the regulation and expression of cyclo-oxygenase 2, inducible NO synthase and argininosuccinate synthetase. We observed different transcriptional regulation of these enzymes depending on the db-cAMP concentration used. Low concentrations of db-cAMP in the range 10-50 microM elevated levels of cyclo-oxygenase 2 mRNA, protein and activity, but not the respective mRNA and protein concentrations of the inducible NO synthase or argininosuccinate synthetase. At higher concentrations a massive induction of the latter two enzymes was also apparent. Expression of prostacyclin synthase and argininosuccinate lyase, secondary enzymes of NO- and prostanoid-forming pathways, was not stimulated by db-cAMP. Prostaglandin E2, known to be an intracellular physiological trigger of cAMP formation, stimulated only cyclooxygenase 2 expression and activity at a concentration of 10 microM, and not inducible NO synthase. The induction of the mRNA for the transcription factors JunB and p65, a component of the NF kappa B complex, by prostaglandin treatment of the cells might be a possible mechanistic explanation for this observation.

Animals↗
PubMed1996

Mixed maternal-paternal lymphocyte cultures before and after immunotherapy for recurrent spontaneous abortions.

PROBLEM: The increased reactivity of maternal lymphocytes in reciprocal mixed-maternal-paternal lymphocyte cultures (MMPLC), observed in the presence of control serum after immunotherapy, suggests that immunization with paternal lymphocytes may induce a highly significant cell mediated immune response in specifically alloactivated maternal lymphocytes. METHOD: Reciprocal one-way MMPLC were set up with responding maternal or paternal lymphocytes and mitomycin C-treated stimulating lymphocytes. Cultures were set up for 6 days in the presence of 15% maternal or control serum. The degree of lymphocyte stimulation was measured by tritiated thymidine uptake. RESULTS: In maternal serum, after immunotherapy, a highly significant blocking effect on MMPLC was observed in both directions. The extent of the blocking effect in maternal serum and the stimulation in control serum was much higher, after immunotherapy, in two cases of abortions, as compared to cases with normal pregnancy outcome. CONCLUSIONS: Although the number of cases is very small, it may be that in abortions, in the presence of maternal serum, disturbances in the balance of cytokines or/and specific antibodies could have cytotoxic effects on MMPLC and down regulate, or "block" the specific response. For a possibly better utilization of the MMPLC test in the prediction of pregnancy outcome after immunotherapy, it may be important to examine specific antibodies in maternal serum, to investigate specifically induced cytokines in MMPLC and to evaluate T cell subsets in MMPLC in the presence of maternal and control serum.

Abortion, Habitual↗
PubMed1996

Correlation between tumour and serum beta 2m expression in patients with breast cancer.

HLA class I antigens are composed of a major histocompatibility complex (MHC) encoded heavy chain that is associated non-covalently with a light chain beta-2 microglobulin (beta-2m). When the HLA complex is metabolized, beta-2m is shed into the serum. A large variety of human and experimental tumours have altered MHC class I expression. In a previous study we observed elevated mean beta-2m serum levels in breast cancer patients, as compared to controls. To study the relationship between tumour expression and serum levels, we examined 54 patients with breast cancer. Tumour beta-2m was determined by immunohistochemistry and serum levels by the ELISA technique. Of the 54 patients, 38 had low and 16 had high beta-2m expression on the tumour. There was a significant correlation between tumour beta-2m and serum beta-2m levels (P = 0.02), with patients whose tumours expressed high beta-2m having high serum beta-2m levels. There was an inverse correlation between tumour grade and tumour beta-2m expression which approached statistical significance (P = 0.06). These findings suggest that in a substantial number of patients the high serum levels derive from shedding of beta-2m from tumour cells. These levels may have implications for tumour growth and metastases due to influences on immunological responses.

Adult↗
PubMed1996

Cyclooxygenase-2-dependent bronchoconstriction in perfused rat lungs exposed to endotoxin.

BACKGROUND: Lipopolysaccharides (LPS), widely used to study the mechanisms of gram-negative sepsis, increase airway resistance by constriction of terminal bronchioles. The role of the cyclooxygenase (COX) isoenzymes and their prostanoid metabolites in this process was studied. MATERIALS AND METHODS: Pulmonary resistance, the release of thromboxane (TX) and the expression of COX-2 mRNA were measured in isolated blood-free perfused rat lungs exposed to LPS. RESULTS: LPS induced the release of TX and caused increased airway resistance after about 30 min. Both TX formation and LPS-induced bronchoconstriction were prevented by treatment with the unspecific COX inhibitor acetyl salicylic acid, the specific COX-2 inhibitor CGP-28238, dexamethasone, actinomycin D, or cycloheximide. LPS-induced bronchoconstriction was also inhibited by the TX receptor antagonist BM-13177. The TX-mimetic compound, U-46619, increased airway resistance predominantly by constricting terminal bronchioles. COX-2-specific mRNA in lung tissue was elevated after LPS exposure, and this increase was attenuated by addition of dexamethasone or of actinomycin D. In contrast to LPS, platelet-activating factor (PAF) induced immediate TX release and bronchoconstriction that was prevented by acetyl salicylic acid, but not by CGP-28238. CONCLUSIONS: LPS elicits the following biochemical and functional changes in rat lungs: (i) induction of COX-2; (ii) formation of prostaglandins and TX; (iii) activation of the TX receptor on airway smooth muscle cells; (iv) constriction of terminal bronchioles; and (v) increased airway resistance. In contrast to LPS, the PAF-induced TX release is likely to depend on COX-1.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

HLA class I antigen expression in human solid tumors.

The expression of HLA class I antigens was studied by immunohistochemistry in various tumors in correlation with clinicopathologic characteristics. Reduced expression was observed in germ cell testicular cancer, kidney, prostate, gastric and colon cancer, and was associated with tumor aggressiveness, grade and penetration of the tumor through the organ wall. In bladder cancer reduced expression was associated with poor survival. Irradiation of brain tumors resulted in an increase in class I expression. Soluble class I levels were studied in breast and colon cancer patients and were found to be high in those with metastatic disease. The clinical relevance of reduced class I levels are discussed.

Gene Expression Regulation, Neoplastic↗
PubMed1995

Suppression of melatonin secretion in some blind patients by exposure to bright light.

BACKGROUND: Complete blindness generally results in the loss of synchronization of circadian rhythms to the 24-hour day and in recurrent insomnia. However, some blind patients maintain circadian entrainment. We undertook this study to determine whether some blind patients' eyes convey sufficient photic information to entrain the hypothalamic circadian pacemaker and suppress melatonin secretion, despite an apparently complete loss of visual function. METHODS: We evaluated the input of light to the circadian pacemaker by testing the ability of bright light to decrease plasma melatonin concentrations in 11 blind patients with no conscious perception of light and in 6 normal subjects. We also evaluated circadian entrainment over time in the blind patients. RESULTS: Plasma melatonin concentrations decreased during exposure to bright light in three sightless patients by an average (+/- SD) of 69 +/- 21 percent and in the normal subjects by an average of 66 +/- 15 percent. When two of these blind patients were tested with their eyes covered during exposure to light, plasma melatonin did not decrease. The three blind patients reported no difficulty sleeping and maintained apparent circadian entrainment to the 24-hour day. Plasma melatonin concentrations did not decrease during exposure to bright light in seven of the remaining blind patients; in the eighth, plasma melatonin was undetectable. These eight patients reported a history of insomnia, and in four the circadian temperature rhythm was not entrained to the 24-hour day. CONCLUSIONS: The visual subsystem that mediates light-induced suppression of melatonin secretion remains functionally intact in some sightless patients. The absence of photic input to the circadian system thus constitutes a distinct form of blindness, associated with periodic insomnia, that afflicts most but not all patients with no conscious perception of light.

Adolescent↗
PubMed1995

Importance of valves and lymphangion contractions in determining pressure gradients in isolated lymphatics exposed to elevations in outflow pressure.

Lymphatic pressures were measured at several locations along an isolated lymphatic system exposed to elevations in outflow pressure. The objective of this study was to determine the contributions of lymphangion contractions and valve function to the observed pressure gradients. In each experiment, five bovine mesenteric lymphatic vessels (each with four to nine lymphangions) were joined in series by t-pieces connected to pressure transducers. The vessels were placed in an organ bath with input provided by a reservoir filled with Krebs solution. With a constant inflow pressure of 4 cm H2O, outflow pressures were elevated in 2- or 5-cm H2O increments. Except for inflow and outflow pressures which were fixed, the pressures measured at four other locations along the system were pulsatile due to lymphatic contractions. The mean pressures increased as outflow pressures were raised. While mean pressures were highest at the outflow end, estimates of the net pressure generated by each segment suggested that all segments, including those at the most upstream locations, increased their contractile activity. In addition, diastolic pressure gradients formed across the system. These did not appear to be due to valve failure (endurance limit of valves was 168 +/- 32 cm H2O) but rather, appeared to relate to the progressive inability of lymphangions to empty which, for a given lymphangion, began to occur at a mean outflow pressure of 9.8 +/- 1.1 cm H2O.

Animals↗
PubMed1995

Regulation of prostanoid-synthesis in the cardiovascular system.

Thromboxane A2 and prostacyclin are the two prostanoids involved in the regulation of the vascular tone. Their release is controlled by the activity of cyclooxygenase which has made this enzyme a preferred pharmacological target. We here report on the distribution of the two isoforms of cyclooxygenase in cultured mesangial cells and on a selective inhibitor of the cytokine-inducible cyclooxygenase-2. We also comment on the structure of thromboxane and prostacyclin synthase and their regulation under physiological and pathophysiological conditions.

Amino Acid Sequence↗
PubMed1995

CMP-N-acetyl neuraminic-acid synthetase from Escherichia coli: fermentative production and application for the preparative synthesis of CMP-neuraminic acid.

In an optimized sorbitol/yeast extract/mineral salt medium up to 12 U/l CMP-N-acetyl-neuraminic-acid (Neu5Ac) synthetase was produced by Escherichia coli K-235 in shake-flask culture. A colony mutant of this strain, E. coli K-235/CS1, was isolated with improved enzyme formation: in shake flasks with a yield of up to 20.8 U/l and 54 mU/mg protein in the cell extract. With this strain 26500 U CMP-Neu5Ac synthetase was produced with a high specific activity (0.128 U/mg) by fed-batch fermentation on 230-l scale. On a 10-1 scale the enzyme yield was 191 U/l culture medium. The enzyme was partially purified by precipitation with polyethyleneglycol resulting in a three- to fourfold enrichment and a recovery rate of more than 80%; most of the CTP hydrolysing enzymes were removed. The native synthetase was deactivated completely by incubation at 45 degrees C for 10 min, but could be stabilized remarkably by glycerol and different salts. The enzyme was used for the preparative synthesis of CMP-Neu5Ac with a conversion yield of 87% based on CTP.

Culture Media↗
PubMed1995

Contribution of class I HLA-A2 antigen in immune reactions.

The involvement of the Class I HLA-A2 antigen is briefly reviewed in relation to allograft rejection, the feto-maternal relationship, viral cytotoxic reactions and tumor immunity. It is suggested that the HLA-A2 molecule may have, as compared to other HLA Class I alleles, a dominant role as a restricting element in cytotoxic T-cell recognition in the feto-maternal relationship to male fetuses, in specific viral infections and in tumors. As compared to other HLA Class I alleles, its reduced expression or loss in a variety of tumors suggests its possible important role in tumor immune surveillance. The disappearance of HLA-A2 from tumor cells may eventually contribute to the escape from T-cell recognition of malignant cells.

Cytotoxicity, Immunologic↗