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V Lehmann

Publications and source records attributed to V Lehmann.

At least 19 recordsLinked to original sources
PubMed1999

Nitric-oxide-induced apoptosis in human leukemic lines requires mitochondrial lipid degradation and cytochrome C release.

We have previously shown that nitric oxide (NO) stimulates apoptosis in different human neoplastic lymphoid cell lines through activation of caspases not only via CD95/CD95L interaction, but also independently of such death receptors. Here we investigated mitochondria-dependent mechanisms of NO-induced apoptosis in Jurkat leukemic cells. NO donor glycerol trinitrate (at the concentration, which induces apoptotic cell death) caused (1) a significant decrease in the concentration of cardiolipin, a major mitochondrial lipid; (2) a downregulation in respiratory chain complex activities; (3) a release of the mitochondrial protein cytochrome c into the cytosol; and (4) an activation of caspase-9 and caspase-3. These changes were accompanied by an increase in the number of cells with low mitochondrial transmembrane potential and with a high level of reactive oxygen species production. Higher resistance of the CD95-resistant Jurkat subclone (APO-R) cells to NO-mediated apoptosis correlated with the absence of cytochrome c release and with less alterations in other mitochondrial parameters. An inhibitor of lipid peroxidation, trolox, significantly suppressed NO-mediated apoptosis in APO-S Jurkat cells, whereas bongkrekic acid (BA), which blocks mitochondrial permeability transition, provided only a moderate antiapoptotic effect. Transfection of Jurkat cells with bcl-2 led to a complete block of apoptosis due to the prevention of changes in mitochondrial functions. We suggest that the mitochondrial damage (in particular, cardiolipin degradation and cytochrome c release) induced by NO in human leukemia cells plays a crucial role in the subsequent activation of caspase and apoptosis.

Apoptosis↗
PubMed1999

Induced metal tolerance in microbenthic communities from three lowland rivers with different metal loads

The response of microbenthic communities to sustained metal stress was studied in three lowland rivers with different levels of pollution. Tolerance against zinc and cadmium was determined in short-term toxicity tests with microbenthic assemblages colonizing glass discs. Photosynthetic activity served as an endpoint in tests for algae, whereas for bacteria thymidine incorporation was determined. For bacterial assemblages from unpolluted locations, EC50 values in short-term tests ranged between 6.7 and 56.2 &mgr;M zinc, and 8.7 and 25.5 &mgr;M cadmium, respectively. Bacterial assemblages from the two most polluted sites were significantly more tolerant for zinc (EC50: 994 &mgr;M and >1,000 &mgr;M) and cadmium (EC50: 218 &mgr;M and 154 &mgr;M). Results indicated a shift in community composition toward pollution-adapted organisms when a threshold concentration of 1 &mgr;M zinc is exceeded. Although an increasing community tolerance was also indicated for algae, EC50 values for microbenthic algae from all sites exceeded in most cases the highest metal concentrations tested (Zn: 1,000 &mgr;M; Cd: 320 &mgr;M). Since species composition of algal assemblages was found to change at much lower metal levels, it is concluded that short-term toxicity tests measuring photosynthesis inhibition do not reflect well the long-term effects of these metals. Toxic effects of metals on both algal and bacterial assemblages are attenuated by precipitation and complexing capacities of the biofilm.

Journal Article↗
PubMed1998

Sesquiterpene lactones specifically inhibit activation of NF-kappa B by preventing the degradation of I kappa B-alpha and I kappa B-beta.

Extracts from certain Mexican Indian medicinal plants used in traditional indigenous medicine for the treatment of inflammations contain sequiterpene lactones (SLs), which specifically inhibit the transcription factor NF-kappa B (Bork, P. M., Schmitz, M. L., Kuhnt, M., Escher, C., and Heinrich, M. (1997) FEBS Lett. 402, 85-90). Here we show that SLs prevented the activation of NF-kappa B by different stimuli such as phorbol esters, tumor necrosis factor-alpha, ligation of the T-cell receptor, and hydrogen peroxide in various cell types. Treatment of cells with SLs prevented the induced degradation of I kappa B-alpha and I kappa B-beta by all these stimuli, suggesting that they interfere with a rather common step in the activation of NF-kappa B. SLs did neither interfere with DNA binding activity of activated NF-kappa B nor with the activity of the protein tyrosine kinases p59fyn and p60arc. Micromolar amounts of SLs prevented the induced expression of the NF-kappa B target gene intracellular adhesion molecule 1. Inhibition of NF-kappa B by SLs resulted in an enhanced cell killing of murine fibroblast cells by tumor necrosis factor-alpha. SLs lacking an exomethylene group in conjugation with the lactone function displayed no inhibitory activity on NF-kappa B. The analysis of the cellular redox state by fluorescence-activated cell sorter showed that the SLs had no direct or indirect anti-oxidant properties.

Animals↗
PubMed1997

Sphingosine-1-phosphate mobilizes intracellular calcium and activates transcription factor NF-kappa B in U937 cells.

Sphingosine-1-phosphate (SPP), a metabolite of sphingolipids, has been implicated as a second messenger in cell growth regulation and signal transduction via calcium mobilization from internal stores. This study shows that SPP mobilizes intracellular calcium in U937 cells and demonstrates for the first time the ability of SPP to activate the transcription factor NF-kappa B in these cells. Furthermore, calcium release from the internal stores by thapsigargin (TG), an inhibitor of the endoplasmic reticulum Ca2+ pump, was associated with activation of NF-kappa B. Moreover, we have shown that while an intracellular calcium chelator BAPTA/AM was able to inhibit both SPP- and TG-induced NF-kappa B activation, it had no effect on TNF-induced NF-kappa B activation. In addition, SPP-induced NF-kappa B activation was blocked both by cyclosporin A, known to inhibit calcineurin phosphatase activity, and by the antioxidant butylated hydroxyanisole. These observations suggest that intracellular calcium mobilization is required for SPP-induced NF-kappa B activation, which may involve calcineurin- and redox-dependent mechanisms.

Antioxidants↗
PubMed1997

Iron chelation decreases human immunodeficiency virus-1 Tat potentiated tumor necrosis factor-induced NF-kappa B activation in Jurkat cells.

TNF-alpha stimulates HIV-1 replication via activation of the transcription factor NF-kappa B. TNF-mediated activation of NF-kappa B is known to involve the intracellular formation of reactive oxygen intermediates (ROIs). We recently demonstrated that HIV-1 Tat protein potentiates TNF-induced NF-kappa B activation by downregulation of manganese-dependent superoxide dismutase (MnSOD), shifting the cellular redox state towards pro-oxidative conditions. This study shows that treatment of Jurkat cells with iron chelator deferoxamine (DFO) strongly decreases HIV-1 Tat-potentiated TNF-induced NF-kappa B activation but does not modify NF-kappa B activation by TNF-alpha. The ability of iron chelators to reduce Tat-potentiated TNF-induced NF-kappa B binding activity suggests that iron and intracellular hydroxyl radicals (OH.) are required for Tat effect. Moreover, we have shown that exogenously generated OH. markedly enhanced TNF-induced NF-kappa B activation in a dose-dependent manner while was not sufficient to trigger activation of NF-kappa B by itself. In addition, iron chelators had no effect either on MnSOD activity or on the decrease of this activity by Tat. Iron chelators had also no effect on the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), but could elevate the GSH:GSSG ratio decreased by Tat protein. These observations suggest that the formation of intracellular OH. in the presence of iron ions play a major role in HIV-1 Tat enhancement of TNF-induced NF-kappa B activation and that iron chelation may protect Jurkat T cells, at least in part, against oxidative stress induced by Tat.

Down-Regulation↗
PubMed1996

HIV type 1 glycoprotein 120 amplifies tumor necrosis factor-induced NF-kappa B activation in Jurkat cells.

This article demonstrates that human immunodeficiency virus type 1 (HIV-1) gp120 amplifies the activity of tumor necrosis factor alpha (TNF-alpha), a cytokine that stimulates HIV-1 replication through activation of NF-kappa B. In CD4-positive Jurkat cells, gp120 potentiates TNF-induced NF-kappa B activation. TNF-mediated activation of NF-kappa B is known to involve the intracellular formation of reactive oxygen intermediates (ROIs). Accordingly, we examined the influence of gp120 on the cellular redox state. We found that gp 120-modulated TNF-induced NK-kappa B activation was inhibited by the antioxidant butylated hydroxyanisole, indicating the involvement of redox-dependent mechanisms. In addition, we showed that gp120 induces intracellular formation of hydrogen peroxide, which is accompanied by a decrease in the ratio of glutathione to glutathione disulfide. In contrast, in the p56lck-deficient J.CaM1.6 T cell line, a derivative of the Jurkat cell line, gp120 was unable to stimulate hydrogen peroxide, to decrease the ratio of GSH to GSSG, and has no effect on TNF-induced NF-kappa B activation. This demonstrated that p56lck protein tyrosine kinase plays an active role in transmitting a signal that increases the oxidative state of the cell and as a consequence amplifies TNF-mediated NF-kappa B DNA binding. We have demonstrated that Tat protein decreased both the Mn-dependent superoxide dismutase (MnSOD) and the cellular glutathione content (GSH). Here we show that, in contrast to Tat, gp120 is unable to inhibit activity and expression of MnSOD and to decrease GSH content. Taken together, our data suggest that gp120 potentiates TNF-induced NF-kappa B activation by stimulating a signal pathway that involves p56lck and the increased formation of reactive oxygen intermediates such as H2O2. These findings may be relevant for the regulation of HIV-1 replication in T cells.

Antioxidants↗
PubMed1996

Induction of NO synthesis in macrophages by Newcastle disease virus is associated with activation of nuclear factor-kappa B.

Newcastle disease virus (NDV) has received much attention recently because of its non-specific immune stimulating potential and its various anti-tumor activities. Here we describe that NDV induces synthesis of NO and causes an activation of nuclear factor-kappa B (NF-kappa B) in murine macrophages. These reactions were part of an activation process which included also stimulation of adenosine deaminase and inhibition of 5'-nucleotidase. NDV-mediated NO synthesis and NF-kappa B activation were blocked by an antioxidant (butylated hydroxyanisole), by an inhibitor of protein tyrosine kinase (genistein) and of protein kinase A (H-89), but not by an inhibitor of protein kinase C (staurosporin). These data suggest that signalling requirements of NF-kappa B activation and NO production in NDV-treated macrophages are similar.

Adenosine Deaminase↗
PubMed1996

S-adenosylhomocysteine as a physiological modulator of Apo-1-mediated apoptosis.

APO-1/Fas (CD95) is a member of the tumor necrosis factor/nerve growth factor receptor superfamily and mediates apoptosis in various cell types. Here we show that L929 cells, expressing human APO-1 treated with agonistic antibodies (anti-APO-1), elicit an early and transient increase of S-adenosylhomocysteine (AdoHcy), a potent inhibitor of S-adenosylmethionine (AdoMet)-dependent methylation reactions. In contrast, anti-APO-1 did not induce an AdoHcy increase in L929-APO-1 Delta4 cells expressing a C-terminally truncated APO-1 lacking part of the 'death domain' known to be required for the transduction of apoptotic signals. Addition of adenosine and D, L-homocysteine also led to an increase of cellular AdoHcy thus enhancing anti-APO-1-induced killing of L929-APO-1 cells. Treatment with anti-APO-1 also induced release of arachidonic acid from phospholipids: this effect was augmented by elevated levels of AdoHcy. In contrast, AdoHcy had only a minor effect on anti-APO-1-mediated DNA fragmentation. These findings suggest that AdoHcy functions as a physiological modulator of APO-1-mediated cell death in L929 cells and enhances anti-APO-1-induced cell killing at least partially by acting via the phospholipase A2 pathway.

Adenosine↗
PubMed1995

HIV-1 Tat potentiates TNF-induced NF-kappa B activation and cytotoxicity by altering the cellular redox state.

This study demonstrates that human immunodeficiency virus type 1 (HIV-1) Tat protein amplifies the activity of tumor necrosis factor (TNF), a cytokine that stimulates HIV-1 replication through activation of NF-kappa B. In HeLa cells stably transfected with the HIV-1 tat gene (HeLa-tat cells), expression of the Tat protein enhanced both TNF-induced activation of NF-kappa B and TNF-mediated cytotoxicity. A similar potentiation of TNF effects was observed in Jurkat T cells and HeLa cells treated with soluble Tat protein. TNF-mediated activation of NF-kappa B and cytotoxicity involves the intracellular formation of reactive oxygen intermediates. Therefore, Tat-mediated effects on the cellular redox state were analyzed. In both T cells and HeLa cells HIV-1 Tat suppressed the expression of Mn-dependent superoxide dismutase (Mn-SOD), a mitochondrial enzyme that is part of the cellular defense system against oxidative stress. Thus, Mn-SOD RNA protein levels and activity were markedly reduced in the presence of Tat. Decreased Mn-SOD expression was associated with decreased levels of glutathione and a lower ratio of reduced:oxidized glutathione. A truncated Tat protein (Tat1-72), known to transactivate the HIV-1 long terminal repeat (LTR), no longer affected Mn-SOD expression, the cellular redox state or TNF-mediated cytotoxicity. Thus, our experiments demonstrate that the C-terminal region of HIV-1 Tat is required to suppress Mn-SOD expression and to induce pro-oxidative conditions reflected by a drop in reduced glutathione (GSH) and the GSH:oxidized GSH (GSSG) ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1995

1H-NMR microscopy of tablets.

A 1H-nuclear magnetic resonance (NMR) microscopy method was utilized for the first time to determine the porosity distribution of physically intact tablets. The main advantage of this newly developed method was that porosity cross sections through whole tablets or specific locations could be obtained without mechanically destroying the tested tablet. This was achieved by filling tablet cavities with silicone oil under vacuum. The amount of silicone oil locally within the tablet was then determined by 1H-NMR microscopy, revealing the inverse inner structure. To reduce the measuring time, a paramagnetic gadolinium complex was added to the silicone oil. The cross sectional signals produced by 1H-NMR microscopy through the tablet were transformed into a color image by a specially designed computer graphic program. To improve the signal-noise ratio an algorithm of 3D-filtering was introduced. The maximal spatial resolution achieved with this method was about 95 microns for a cube's edge length corresponding to some 380,000 positions in a 9-mm-diameter compression-coated tablet. Uneven porosity distributions within tablets, cracks, or cavities could be visualized with this newly developed method. Different compaction mechanisms were observed with plastic- or brittle-type tablets. The different states of densification during compaction of powders could be detected. The integrity of compression coatings was determined to be dependent on the pressure load and the location of the core within the coat.

Magnetic Resonance Imaging↗
PubMed1994

Adenosine and homocysteine together enhance TNF-mediated cytotoxicity but do not alter activation of nuclear factor-kappa B in L929 cells.

This paper shows that a combination of adenosine and homocysteine potentiates TNF-alpha-mediated cytotoxicity, but does not modulate activation of NF-kappa B transcription factor controlling the expression of various TNF-alpha-inducible genes. Adenosine and homocysteine at concentrations (1 mM each) that enhance TNF-alpha-induced cytotoxicity accumulate S-adenosyl-L-homocysteine (AdoHcy), a potent inhibitor of S-adenosyl-L-methionine-dependent methylation reactions. In addition, preloading L929 cells with AdoHcy resulted in enhanced responses to TNF-alpha, suggesting that AdoHcy potentiates TNF-alpha-induced cytotoxicity. Moreover, the combination of adenosine and homocysteine changed the dependency of the TNF-alpha-mediated cytolysis on reactive oxygen intermediates. In the absence of adenosine and homocysteine TNF-alpha-mediated cytotoxicity was inhibited by antioxidants such as butylated hydroxyanisole and pyrrolidine dithiocarbamate. In the presence of adenosine and homocysteine, however, TNF-alpha-mediated cytotoxicity is not inhibited by these antioxidants. A L929 subclone, defective in the respiratory chain, resisted the cytotoxic action of TNF-alpha, but was rendered TNF-alpha sensitive in the presence of adenosine and homocysteine. Unlike TNF-alpha-mediated cytotoxicity, the TNF-alpha-induced activation of NF-kappa B was inhibited by antioxidants regardless whether adenosine and homocysteine were present or absent in the culture medium. In conclusion, a combination of adenosine and homocysteine selectively modulates TNF-alpha-mediated cytotoxicity without changing the TNF-alpha-induced activation of NF-kappa B. Our results could facilitate the development of strategies that permit dissection of cytotoxic and gene-activating pathways.

Adenosine↗
PubMed1993

[Magnetic resonance microscopy--new prospects for endodontics].

With the use of magnetic resonance microscopy (MRM) the options and limitations of this modern technique in reproducing teeth and endodontium should be evaluated. Therefore, extracted teeth were stored in formaline and measured in two different devices of the magnetic resonance technique. One is common for material research and normally used for spectroscopy of solids. Measuring takes place in the strayfield of the magnet which leads to the term "Stray Field Imaging" (STRAFI). The other one is a spectroscopy with an additional micro-imaging device (magnetic resonance microscope) where resolutions up to (100 microns)3 can be reached. For the first time the STRAFI allowed to make pictures from the hydrogen-protons of the teeth's hard substances. A two or three dimensional imaging on the basis of microscopic resolution became reality. In addition the MRM allowed to depict the soft tissue portion and the outer contour of the teeth in 2D and 3D. The two-dimensional pictures were able to show a texture within the pulp tissue. The three-dimensional images enabled a naturalistic and non-destructive visualization of the outer surface and the pulp room. The results shown here open very new perspectives for endodontics.

Dental Pulp Cavity↗
PubMed1992

Cross-reacting serum opsonins in patients with meningococcal disease.

We have examined the opsonic activity of sera from patients with Neisseria meningitidis (B:15:P1.16) infections against different meningococcal strains, using flow cytometry and luminol-enhanced chemiluminescence. A marked increase in the phagocytosis of ethanol-fixed meningococcal strains of different serogroups, serotypes, and serosubtypes was demonstrated in the presence of convalescence sera compared with acute sera. Convalescence sera also caused a significant increase of leukocyte oxidative metabolism during phagocytosis, as measured by luminol-enhanced chemiluminescence. The sera contained a broad range of opsonins cross-reacting with serogroup A, B, C, W-135, and Y meningococci of different serotypes and serosubtypes, indicating that the cross-reacting opsonins recognized surface epitopes other than those determined by current serotyping schemes.

Adolescent↗
PubMed1992

Monocyte phagocytosis of opsonized Neisseria meningitidis serogroup B.

The chemiluminescence (CL) was examined when peripheral blood monocytes were incubated with opsonized Neisseria meningitidis, serogroup B, serotype 15:P1.16 or serotype 2a:P1.2. The monocytes were separated from a mononuclear cell suspension by an immunomagnetic negative selection technique using magnetic polystyrene microspheres coated with monoclonal antibodies specific for T and B lymphocytes. More than 90% of the lymphocytes were removed, yielding a suspension containing 93% monocytes. Optimal sensitivity for phagocytosis was obtained using 1% serum (10 microliters), 72 bacteria per monocyte cell, and 7.5 min opsonization and incubation time during continuous agitation at 37 degrees C. The CL was amplified by lucigenin. Preliminary experiments suggest that convalescent sera from patients with group B meningococcal disease induced increased CL responses compared to acute sera. Sera from volunteers immunized with an outer membrane complex vaccine from serogroup B, serotype 15:P1.16 or 2a:P1.2 meningococci also induced increased CL activity compared to preimmune sera. No such response was shown when a group B capsular polysaccharide vaccine was given. This response pattern was also demonstrated by a flow cytometric phagocytosis technique (FCM). Internalization of meningococci by monocytes was demonstrated by a FCM quenching technique and by transmission electron microscopy. CL and FCM represent rapid and reproducible methods for the measurement of opsonophagocytosis of meningococci by monocytes and may be performed with minute amounts of sera.

Adult↗